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- 1. CHAPTER 5 Writing and Solving Equations M A T H Chapter Vocabulary numerical expression evaluate order of operations variables value equation inequality solution formula 5.1 Numerical Expressions and Order of OperationsA numerical expression contains numbers and operation symbols. Toevaluate a numerical expression means to perform the operationsshown to obtain a single numerical value. To evaluate an expressionwith more than one operation, use this order of operations. • Perform all calculations within parentheses, brackets, or above or below the division bar. • Do all calculations involving exponents or roots. • Multiply or divide, in order, from left to right. • Add or subtract in order, from left to right. 139
- 2. Model Problems 1. Simplify. a. 9 3 2 7 b. 12 3 5 8 Solution a. 9 3 2 7 b. 12 3 5 8 9 6 7 4 5 8 3 7 4 40 10 44 2. Simplify 6 4 (8 32). Solution 6 4(8 32) Simplify exponent. 6 4(8 9) Add in parentheses. 6 4(17) Multiply. 6 68 Add. Answer 74 3. Find the value of 31 28 2 10. 7 "9 Solution 31 28 2 10 Simplify square root. 7 "9 31 28 2 10 Subtract below division bar. 7 3 31 28 2 10 Divide and multiply. 4 31 7 20 Add. 38 20 Subtract. Answer 18 4. The cost of a regular admission to the museum is $6.00. The cost of a student admission is $4.00. Write an expression for the amount of money that will be collected from 28 regular admissions and 53 student admissions. Evaluate the expression. Solution Write an expression for the regular admissions. 28 6 Write an expression for the student admissions and add it to the prod- uct above. 28 6 53 4 Use the order of operations to evaluate. 28 6 53 4 Multiply first. 168 212 Add. 380 Answer The amount collected is $380.140 Chapter 5 • Writing and Solving Equations
- 3. Practice1. Evaluate 23 15 6 3. 9. Each box of candy contains 24 caramels and 18 creams. Which expression shows A. 20 B. 42 the total number of candies in 12 boxes? C. 50 D. 96 A. 12 24 182. Evaluate 72 23 45 17 . B. 12 (24 18) 7 C. (12 24) 18 A. 6 B. 13 D. (12 18) 24 C. 15 D. 40 10. For which expression would the first3. The value of 62 2 9 3 is equal to step be to multiply? A. 1.5 B. 5 A. 100 ÷ 2 5 21 C. 57 D. 165 B. (8 7) 3 194. Simplify the expression: C. "25 4 6 3 40 2 Q5 "4R. D. 5 9 8 2 3 11. Write the operation you would per- A. 13 1 B. 21 3 form first. C. 23 D. 43 a. 9 7 15 4 18 . b. 14 ÷ 2 16 95. Evaluate 122 9 6 10 7 c. (11 7) 6 ÷ 3 A. 39 B. 63 d. 100 ÷ 52 15 4 C. 84 D. 96 12. Simplify.6. Which expression is equal to 2? a. 20 8 ÷ 2 3 A. 24 (2 2) 5 b. 36 ÷ 4 5 3 B. (24 2) (2 5) c. 19 4 3 5 d. 14 5 6 ÷ 6 C. (24 2 2) 5 D. 24 (2 2 5) 13. Find the value of each expression.7. Which expression is equal to 1? a. 9 (8 2) ÷ 6 b. (8 12) 4 6 A. 64 ÷ 8 ÷ 2 6 c. 45 ÷ (3 5) 5 B. 64 ÷ 8 ÷ (2 6) d. (4 3)2 3 1 C. 64 ÷ (8 ÷ 2) 6 D. (64 ÷ 8 ÷ 2) 6 14. Evaluate each expression.8. Admission to a state fair is $5 and each a. 48 "64 23 13 2 ride costs an additional $2. Which ex- b. 22 "121 (4 7) pression shows the cost of admission c. 4 53 52 3 to the fair and 7 rides? 2 2 5 2 A. (5 7) 2 B. 7 2 5 d. 7 9 3 C. 7 2 5 D. 7 (2 5) 24 11 2 Numerical Expressions and Order of Operations 141
- 4. 15. Rewrite each sentence using parenthe- 18. Shavel has $65. She wants to purchase ses to make it true. a pair of jeans for $32, three tank tops for $14.50 each, and one pair of socks a. 40 ÷ 5 2 3 18 priced at 3 for $7.53 (prices include b. 72 ÷ 7 2 5 40 tax). How much more money does she c. 8 3 9 2 55 need? d. 18 9 3 ÷ 9 23 1 19. Isaac had $280 in his checking ac- count. He wrote 3 checks for $20 each and 2 checks for $75 each. Then heConstructed-Response made a deposit of $110. How muchQuestions money was in his account then?16. Write a numerical expression for the 20. Angela practices piano for 5 hours on sum of six and fourteen, multiplied by Sundays and for 3 hours on all other the difference of ten and seven. Evaluate. days of the week. How many hours does Angela practice in one year?For problems 17–20, write and evaluate anexpression to solve the problem.17. The Paramount Theater charges $8 for adults and $4.50 for children under 12. The cost of parking is $6 per car. What is the total cost for a group of 3 adults and 5 children that came in 2 cars? 5.2 Writing Algebraic ExpressionsIn algebraic expressions, letters called variables are used to representnumbers. x 4 (a b) 10 x is a variable a and b are variables • Verbal phrases can be translated into algebraic expressions by using variables, numbers, and operation signs. • The unknown quantity can be represented by any variable. First letters of key words are often used. • A dot, parentheses, or no symbol is used for multiplication to avoid confusing the variable x with the multiplication sign . • Complicated expressions may require parentheses or other group- ing symbols.142 Chapter 5 • Writing and Solving Equations
- 5. Examples1. Translate each verbal phrase into an algebraic expression. a. the sum of a number (n) and 25 n 25 b. 5 points less than your grade (g) g 5 c. 7.5 centimeters more than the plant’s height (h) h 7.5 d. Adam’s age (a) divided by 3 a÷3 e. the dog’s weight (w) decreased by 2 pounds w 2 f. 3 times the cost (c) of an item 3 # c or 3(c) or 3c2. Translate each verbal phrase into an algebraic expression. a. twice the sum of y and 3 2(y 3) b. the difference of 100 and n, divided by 3 100 n or (100 n) 3 3 c. 8 more than 3 times a number x, doubled 2(3x 8) The use of commas can change the meaning of an expression. the sum of 60 and a number multiplied by 2 60 2n the sum of 60 and a number, multiplied by 2 2(60 n) Practice1. Which is an algebraic expression? 3. Which expression means a number de- creased by 10? A. 3 8 4 2 B. 62 (3 9) A. 10 n C. 2(y 14) 1 B. n 10 D. 2.81 105 C. n 102. Which expression means 9 more than a D. 10 n number? 4. Which expression means the sum of A. 9n twice a number and 5? B. n 9 A. 2(5) n C. 9 n B. 2(n 5) D. n 9 C. 5(2n) D. 2n 5 Writing Algebraic Expressions 143
- 6. 5. Which expression means 7 less than a 10. Use the variable n to translate each number, divided by 4? phrase into an algebraic expression. A. 7 n B. (n 7) 4 a. 2 of a number 4 3 C. n (7 4) D. (7 n) 4 b. 70 divided by a number 6. The expression 3n 2 could be used to c. a number divided by 16 translate which expression? d. the product of a number and 10 A. 2 less than the product of 3 and a 11. Write each expression algebraically. number Use the variable x. B. the product of 3 and 2 less than a a. 7 times the sum of a number and 3 number b. 1 less than 2 times a number C. a number minus the product of 3 c. the difference between a number and 2 and 5, divided by 8 D. the product of a number and 2 less d. the sum of a number and 4, multi- than 3 plied by the difference between the 7. The expression 50 (n 4) could be number and 6 used to translate which expression? 12. Write a verbal phrase for each. A. the quotient of 50 and a number, a. n 12 b. 20 b increased by 4 c. 5(w 4) d. 100 (x y) B. 50 plus 4, divided by a number C. 50 divided by the sum of a num- 13. Nicole is y years old. Write an expres- ber and 4 sion for each. D. the sum of a number and 4 divided a. twice as old as Nicole by 50 b. 3 years older than Nicole 8. Gina sells bracelets for $4 apiece. c. half Nicole’s age Which expression shows how much d. 5 years younger than Nicole Gina will earn if she sells b bracelets? 14. Javon sells plants for d dollars apiece. A. 4 b Write an expression for each. B. 4b a. the cost of 5 plants C. b 4 b. one-third the cost of 10 plants D. 4(b 1) c. 3 dollars more than the cost of 4 9. Write an expression for each. plants d. double the cost of 9 plants a. 15 times a number n b. a weight w divided by 8 15. The length of a room is l feet. Write an c. 3 years less than Kate’s age a expression for each. d. 11 points more than Don’s grade g a. 1 foot less than twice the length b. 8 feet more than the length, divided by 5 c. 40 feet minus 3 times the length d. 6 feet more than 1 the length 4144 Chapter 5 • Writing and Solving Equations
- 7. 5.3 Evaluating Algebraic ExpressionsEach number a variable can represent is a value of the variable. Toevaluate or find the value of an algebraic expression, replace the vari-ables by their numerical values. Then perform the operations that areshown using the correct order of operations as explained in Section5.1. Model Problems 1. Find the value of 20 x when x 9. Solution Replace x with 9 to find a value of 20 x. 20 9 11 Answer When x 9, 20 x 11. 2. Evaluate 3 4a when a 7. Solution Replace a with 7. 3 4( 7) Multiply first. 4( 7) means 4 ( 7). 3 ( 28) Then add. 25 Answer When a 7, 3 4a 25. 3. Evaluate 3s 2t 1 when s 10 and t 4. Solution Replace both variables in the expression with the values given. 3(10) 2(4) 1. Multiply first. 30 8 1 Add and subtract from left to right. 22 1 23 Answer When s 10 and t 4, 3s 2t 1 23. Evaluating Algebraic Expressions 145
- 8. 4. A machine makes 72 copies per minute. Write an expression for the number of copies in m minutes. Then find how many copies can be made in 3.5 minutes. Solution The machine makes 72 copies for each minute. So, in 1 minute it makes 72(1) copies. In 2 minutes it makes 72(2) copies. To find the number of copies, you multiply 72 by the number of minutes. This can be seen in the table below, where the variable m represents the number of minutes. Minutes 1 2 3 3.5 m Number of Copies 72(1) 72(2) 72(3) 72(3.5) 72(m) Evaluate the expression 72(m) for m 3.5. 72(3.5) 252 Answer The machine can make 252 copies in 3.5 minutes. Practice 1. When n 18, the value of 3n 11 is 6. When x 13 and y 7, which expres- sion is equal to 27? A. 54 B. 43 C. 33 D. 15 A. 2x y B. x 2y 2. When c 3, the value of c2 5c 1 is C. 3x 3y A. 15 B. 19 D. 2(x y) 1 C. 25 D. 55 7. When m 16 and n 4, which expres- 3. Evaluate 4x 3y if x 16 and y 12. sion is equal to 7? A. 0 B. 4 A. (m n) 6 C. 16 D. 28 B. m 2n 1 C. (2m 3) (n 1) 4. Find the value of 2s 5t 1 when s D. m n2 3 7 and t 2. 8. When w 5, x 4, y 15, and z 7, A. 5 B. 25 which expression cannot be evaluated? C. 32 D. 50 5. Evaluate m 1 (3n 4) when m 5 A. 5 x w z 2 and n 12. B. 2(y 15) C. y2 10w 20x A. 15 B. 23 C. 25 D. 45 D. 3 x z 7146 Chapter 5 • Writing and Solving Equations
- 9. 9. Evaluate each expression, using the 13. Jacob is h inches tall. Write an expres- given values of the variables. sion for each height. Then evaluate each expression if Jacob is 63 inches a. 2n 5 when n 2.6 tall. b. 100 7x when x 15 c. 14 3y 9 when y 4 a. 10 inches more than 1 Jacob’s height 3 d. 3z 5 when z 8 b. 19 inches less than twice Jacob’s10. Evaluate each expression using the val- height ues y 11 and z 5. c. 1.5 times Jacob’s height d. Jacob’s height plus 17 inches, di- a. y 2z b. 4z y 3 vided by 5 10(y z) c. y2 z2 d. 14. Complete the table. z 111. Find the value of 3x 2y using the x y y (x 3) 2(x y) given values of the variables. a. 4 9 a. x 2, y 3 b. 12 7 b. x 6, y 10 c. x 32, y 41 c. 8 5 3 2 d. x 7.2, y 0 d. 20 11 15. At the Sport Quench drink factory, a machine fills 40 bottles per minute.Constructed-ResponseQuestions a. How many bottles does the machine fill in m minutes?12. For what value(s) of p could the ex- b. How many bottles does the machine fill in 3 minutes? pression 2100 NOT be evaluated? p 16 c. How many in 1 1 hours? Explain how you arrived at your answer. 2 d. How many in 24 seconds? 5.4 Writing Equations and InequalitiesEquations and inequalities are algebraic sentences. An equation is asentence with an equal sign ( ). An equation states that two quantitiesare equal. An inequality is a sentence with an inequality symbol ( , , , , ). An inequality states that two quantities are unequal. Writing Equations and Inequalities 147
- 10. Inequality Symbols greater than less than greater than or equal to less than or equal to not equal to A solution to an equation or inequality is a value of the variable thatmakes the sentence true. Model Problems 1. Tell whether the given value is a solution of the equation x 9 21. a. 30 b. 12 Solution Replace x with the given value. a. x 9 21 30 9 21 21 21 is true 30 is a solution to the equation x 9 21. b. x 9 21 12 9 21 3 21 is false 12 is not a solution to the equation x 9 21. 2. Tell whether 4 is a solution of each inequality. a. y 3 6 b. 9 y 3 Solution a. y 3 6 4 3 6 7 6 false 4 is not a solution to the inequality y 3 6. b. 9 y 3 9 4 3 5 3 true 4 is a solution to the inequality 9 y 3.148 Chapter 5 • Writing and Solving Equations
- 11. To write an equation or inequality to replace a relationship stated inwords, choose a variable to represent the unknown quantity. Translatethe words of the sentence into algebraic expressions. Examples 1. A number n increased by 13 equals 47. n 13 47 2. The sum of a number m plus 8 is greater than 25. m 8 25 3. $5 more than the cost c is $33. c 5 33 4. 6 pounds less than twice the weight w equals 40 pounds. 2w 6 40 5. 20 miles more than the distance d is less than or equal to 115 miles. d 20 115 6. Three times Jack’s age a subtracted from 100 is 16. 100 3a 16 7. 9 more than half a number n is greater than 12. n 9 12 2 Practice 1. Which number is a solution of x 17 5. Which equation says the cost of sweater 39? s is $10 more than the cost of vest v? A. 12 B. 22 A. s v 10 C. 56 D. 66 B. s 10 v C. s v 10 2. Which number is a solution of 2y 3 D. 10 v s 5? 6. Which sentence says 20 miles more A. 0 B. 2 than twice the distance d is less than C. 4 D. 6 150 miles? 3. Which equation has a solution of 8? A. 2d 20 150 A. x 5 13 B. 2x 2 21 B. 2d 20 150 C. 3x 9 15 D. 20 2x 4 C. 20 150 2d D. 2d 20 150 4. Which equation says 12 more than twice a number n is 38? 7. The sentence x 1 x is A. 2n 12 38 A. true only for the value 0 B. 2n 38 12 B. false only for the value 1 C. 38 2n 12 C. true for all whole numbers D. 2n 38 12 D. false for all whole numbers Writing Equations and Inequalities 149
- 12. 8. Which equation could be used to solve Constructed-Response this problem? Questions Ted’s age 5 years ago was 13. What is Ted’s age t now? 12. On a test, Joan scored 23 points more A. t 5 13 than Vincent did. Joan scored 91 B. t 5 13 points. C. t 13 5 a. Write an equation that can be used D. t 13 5 to find the number of points r that 9. Tell whether the given value is a solu- Vincent scored. tion of the given sentence. b. Which of the values 64, 68, or 78 is Vincent’s score? a. x 12 17, x 5 b. y 3 10, y 7 13. A stack of quarters is worth $9.25. Use c. 2x 3 21, x 12 the equation 0.25n 9.25 and these d. 100 3n 10, n 30 values for n: 35, 36, 37. Find n, the number of quarters in the stack.10. Tell which of the given values is a solu- tion of the given sentence. 14. A jacket was on sale for 3 of its regular 4 price. The sale price was $69. a. 2x 11 29; x {9, 10, 11} b. 3y 12 33; y {14, 15, 16} a. Write an equation that can be used c. 101 m 47; m {147, 148, 149} to find the regular price p. d. c 1 0; c { 4, 3, 2} b. Which of the values $84, $88, $92 is 4 the regular price?11. Write an algebraic sentence for each. 15. The sum of money Lance and Kyra col- a. A number n decreased by 7 is 25. lected for charity equals the sum b. When 8 is subtracted from twice a collected by Marcus and Noelle. Kyra number x, the result is 44. collected $57, Marcus collected $46, c. Ten more than 3 times a number m and Noelle collected $63. is less than 61. a. Write an equation that can be used d. One-half of the product of a number to find l, the amount that Lance col- n and 5 more than the number lected. equals 33. b. Use any method you wish. Find how much Lance collected.150 Chapter 5 • Writing and Solving Equations
- 13. 5.5 Solving Equations with One OperationRecall that addition and subtraction are inverse operations and multi-plication and division are inverse operations. An operation followed byits inverse operation always results in the original number or variable. Start with x → Add 5 to get x 5 → Subtract 5 to get x 5 5 x 3y Start with y → Multiply by 3 to get 3y → Divide by 3 to get y 3 To solve an equation, look at what operation has been used. Thenperform the inverse operation to get the variable by itself on one side.Always use the same inverse operation on both sides of the equation tokeep the equation balanced. Check the solution by substituting in theoriginal equation. Model Problems 1. Solve: x 13 32. Solution The equation shows a number added to x. Use the inverse of adding 13 to solve. 13 x 13 32 x 13 13 32 13 Subtract 13 from both sides of the equation. Answer x 19 Check Replace x in the original equation with 19. Check x 13 32 Check 19 13 32 Check 19 32 32 2. Solve: 27 y 18. Solution Since y has 18 subtracted from it, use the inverse of subtract- ing 18. Add 18 to both sides. 27 18 y 18 18 Answer 45 y Check 27 y 18 Check 27 45 18 Check 27 27 Solving Equations with One Operation 151
- 14. 3. Four times a number is equal to 66. Find the number. Solution Translate the word problem into an equation, and then solve. 4n 66 Use the inverse of multiplying by 4. 4n 66 4 4 Answer n 16.5 Check 4n 66 Check 4(16.5) 66 Check 66 66 4. A florist divided a shipment of roses equally among 8 vases. There were 18 roses in each vase. How many roses were in the shipment? Write and solve an equation. Solution Let r represent the number of roses in the shipment. r 18 Use the inverse of dividing by 8. 8 8 # r 18 # 8 Multiply both sides by 8. 8 Answer r 144 Check r 18 8 Check 144 18 8 Check 18 18 5. Copies of a math workbook are 3 inch thick. How many can be stored 4 on a shelf that is 21 inches wide? Write and solve an equation. Solution Let c number of copies. 3 c 21 4 When an equation involves a variable that is multiplied by a fraction, the reciprocal of the fraction can be used to solve the equation. 3c 21 The reciprocal of 3 is 4 . Multiply both sides 4 4 3 by the reciprocal. 4 Q 3 cR 4 Q 217 R Recall that the product of a fraction and its 3 4 31 1 reciprocal is 1. (1)c 28 Answer c 28 Check 3 (28) 21 4 Check 3 Q 287 R 21 21 41 1 1152 Chapter 5 • Writing and Solving Equations
- 15. Practice1. 6 37 6 7. Solve: 16y 12. A. 6 1 A. 192 B. 4 6 3 B. 36 C. 11 D. 3 4 C. 37 D. 222 8. Which of the following is true about Bart’s solution?2. What is the solution to 34 n 109? Barts Solution A. 65 B. 75 C. 143 D. 1533. Solve: y 28 49. A. 21 B. 77 C. 21 D. 774. Find the solution: y 5 65. A. 13 B. 60 C. 70 D. 3255. Nine times a number n equals 423. Which shows the equation for this A. The solution is correct. problem and its solution? B. He should have added 17 to the left side. A. 9 n 423; n 414 C. He should have subtracted 17 from B. n 423 9; n 3,807 the right side. C. 9n 423; n 47 D. He should have subtracted 43 from D. n 9 423; n 431 both sides.6. Solve: D 9.6 3.7. 9. Solve: 3 t 24. A. 13.3 8 B. 5.9 A. 9 B. 64 C. 5.9 C. 72 D. 192 D. 13.3 10. Which equation has no solution? A. x 1 0 B. x 1 1 C. 1 x 1 D. x 1 x Solving Equations with One Operation 153
- 16. 11. Solve and check each equation. 15. After Helena spent $46 for a pair of sneakers, she had $19 left. How much a. x 29 62 b. y 23 23 money did she have to begin with? c. 4t 10.8 d. m 3.9 312. Write an equation for each sentence. Use n as the variable. Then find the number. a. A number increased by 38 equals 84. b. 5 7 less than a number is 4 1 . 8 2 c. When a number is multiplied by 7, the result is 105. d. One-sixth of a number is 11.8. 16. Steve’s friend gave him 35 baseball13. Solve and check each equation. cards, so Steve had 113 cards. How many cards did Steve have before his a. 2 x 8 b. 5 c 30 friend’s gift? 5 6 17. Monica earned $98.60 working for an c. 2 1 n 45 d. 10 w 50 2 3 hourly wage of $6.80. How many hours did Monica work? 18. So far, Nick has addressed 73 envel-Constructed-Response opes. This is one-eighth of the numberQuestions he must complete. How many envel-For problems 14–19: opes will Nick address in all?a. Assign a variable to the unknown quantity. 19. Takeya has read 302 pages of the novelb. Write an equation you can use to find Oliver Twist. That is 58 pages more the unknown quantity. than César has read. How many pagesc. Solve the equation you wrote to find the has César read? unknown quantity. Show your work. 20. Solve each equation.14. A certain number decreased by 8 is equal to the product of 2 and 6. Find a. x 9 15 b. 2x 18 30 the number. c. 1 x 3 5 3 What do you notice about the solutions? What do you notice about the equations? State any conclusions you might draw. 5.6 Solving Equations with Two OperationsSome equations, like 5x 11 46, require two inverse operations for theirsolution. If you look closely at 5x 11 46, you can see that the x is mul-tiplied by 5 and has 11 added to it. Because there are two operations being154 Chapter 5 • Writing and Solving Equations
- 17. performed on x, you will have to perform two inverse operations to findthe solution. To solve such equations, first work on the addition or sub-traction. Then work on the multiplication or division. Model Problems 1. Solve and check: 5x 11 46. Solution 5x 11 46 Use the inverse of the addition. 5x 11 11 46 11 Subtract 11 from both sides. 5x 35 Then use the inverse of multiplication. 5x 35 Divide both sides by 5. 5 5 Answer x 7 Check 5x 11 46 Check 5(7) 11 46 Check 35 11 46 Check 46 46 2. If one-fourth of a number is decreased by 9, the result is 5. Find the number. Solution Let n represent the number. 1n 9 5 4 1n 9 9 5 9 Use the inverse of subtraction. 4 1 n 14 Use the inverse of multiplying by 1 . 4 4 Remember that dividing by 1 is the same as 4 multiplying by the reciprocal of 1 , that is, 4. 4 4Q 1 nR 4(14) 4 Answer n 56 Check 1n 9 5 4 Check 1 (56) 9 5 4 Check 14 9 5 Check 5 5 Solving Equations with Two Operations 155
- 18. 3. Solve and check: 8(x 7) 24. Solution The first step is to use the distributive property to simplify the left side. 8(x 7) 24 Multiply each term in parentheses by 8. 8x 56 24 8x 56 56 24 56 Subtract 56 from both sides. 8x 32 8x 32 Divide both sides by 8. 8 8 Answer x 4 Check 8(x 7) 24 Check 8( 4 7) 24 Check 8(3) 24 Check 24 24 Practice 1. Which equation has the same solution 4. Solve: 11z 9 79. as 3x 5 16? A. 8 A. 2x 4 15 B. 6 B. 3x 21 C. 7 C. 3x 11 D. 8 D. 1 x 21 5. Solve: 4(x 3) 72. 3 2. Which equation has the same solution A. 15 B. 18 as c 5 34? C. 21 4 A. 4c 10 34 D. 75 4 B. c 39 6. Solve: 5(3x 1) 55. 4 C. c 20 136 A. 4 D. c 29 B. 11 4 C. 18 3. Solve: 8x 3 51. D. 92 A. 6 7. Which equation has a solution of 2? B. 7 C. 6 A. 3(x 2) 0 D. 9 B. 5(2x 1) 0 C. 7(x 2) 0 D. 9(x 4) 0156 Chapter 5 • Writing and Solving Equations
- 19. 8. What is true about Lisa’s solution? 11. Write an equation to solve each prob- Lisas Solution lem. Use n for the variable. Then find the number. a. If 3 times a number is decreased by 7, the result is 32. b. If one-half of a number is increased by 10, the result is 5. c. The sum of 8.7 and 4 times a num- ber is equal to 33.1. d. When 2 is added to a number and the sum is multiplied by 5, the re- sult is 40. Constructed-Response Questions For problems 12–16: a. Assign a variable to the unknown quan- tity. b. Write an equation you can use to find the unknown quantity. c. Solve the equation you wrote to find the A. The solution is correct. unknown quantity. Show your work. B. She should have subtracted 12 on 12. It costs $28 per day plus $0.16 per mile the right. to rent a car. Julia’s charge for a one- C. She should have gotten 25 on the day rental was $69.60. How many right. miles did Julia drive? D. She should have multiplied 5x by 5. per ABC CAR RENTAL $28 day 9. Solve each equation and check. a. 4w 9 77 b. 8c 12 40 c. 1 x 6 10 2 d. 2 m 1 15 13. Rosa, Mel, and Kathy work as a clean- 3 ing crew. They shared the money they10. Solve each equation and check. earned last week equally. Mel spent $26, leaving him with $45. How much a. 5(z 3) 30 money did the crew earn last week? b. 1 (y 8) 12 14. Peter bought a coat at an end-of-winter 4 c. 3(2y 5) 51 half-price sale. Sales tax of $6.24 was d. 7(2x 3) 49 added to the sale price, bringing the cost of the coat to $84.24. What was the original price of the coat? 15. This week, the price of a round-trip train ticket to the city rose by $1.50. Mr. Logan bought 6 tickets and paid $64.50. How much did the round-trip ticket cost before the increase? Solving Equations with Two Operations 157
- 20. 16. Together, Zoë and Susan were planning make twice as many bracelets as she to make 72 bracelets for a craft sale. originally promised to make. How Zoë made 26, then cut her finger and many bracelets had Susan promised to could not work anymore. Susan had to make? 5.7 Graphing and Solving InequalitiesMost of the equations you have solved have had only one solution. Aninequality may have an infinite number of solutions. Since these solu-tions are real numbers, they can be graphed on a number line. Sometypical graphs are shown below. Examples Inequality Description Graph of Solution x 3 All numbers greater than 3 –3 –2 –1 0 1 2 3 4 5 6 x 3 All numbers greater than or –3 –2 –1 0 1 2 3 4 5 6 equal to 3 x 3 All numbers less than 3 –3 –2 –1 0 1 2 3 4 5 6 x 3 All numbers less than or –3 –2 –1 0 1 2 3 4 5 6 equal to 3 1 x 6 4 All the numbers between 1 –3 –2 –1 0 1 2 3 4 5 6 and 4, including 1 but not including 4 To solve an inequality means to describe all the numbers that makethe inequality true. To solve an inequality with several operations, fol-low the same rules as for solving equations, with one importantexception: • When multiplying or dividing both sides of an inequality by a neg- ative number, reverse the direction of the inequality. Example 4 2, but if both sides of the inequality are multiplied by 3, theinequality symbol must be reversed. 3( 4) 3(2) 12 6158 Chapter 5 • Writing and Solving Equations
- 21. Model Problems1. Solve and graph x 7 3. Solution x 7 3 x 7 7 3 7 Answer x 4 –5 –4 –3 –2 –1 0 1 2 3 4 Check Substitute a value greater than 4 in the original inequality. x 7 3 0 7 3 0 7 32. Solve and graph 2y 6. Solution 2y 6 2y 6 Divide each side by 2. Reverse the direction 2 2 of the inequality. Answer y 3 –6 –5 –4 –3 –2 –1 0 1 2 3 4 Check Substitute a value less than 3 in the original inequality. 2y 6 2( 5) 6 10 63. Ilona wants to buy some hair barrettes that cost $3 each. She has also decided to buy a scarf for $8. She does not want to spend more than $22 total. Write and solve an inequality to express the number of barrettes she can buy. Solution The phrase not more than $22 means less than or equal to $22. Let b number of barrettes. 3b 8 22 3b 8 8 22 8 Use the inverse of adding 8 first. 3b 14 3b 14 Then use the inverse of multiplying by 3. 3 3 Do not reverse the inequality. b 42 3 Answer Ilona can buy, at most, 4 barrettes. Graphing and Solving Inequalities 159
- 22. Practice 1. Which value is NOT a solution of 4x 6. What is the solution to m 6 1? 6 50? A. m 7 A. 11 B. 12 B. m 7 C. 20 D. 50 C. m 7 D. 7 m 0 2. What is the inequality that is repre- sented by the graph? 7. What is the solution to 4x 20? A. x 5 –5 –4 –3 –2 –1 0 1 2 3 4 5 B. x 5 A. x 4 B. x 4 C. x 5 C. 4 x 5 D. x 4 D. 5 x 5 8. What is the solution to 5y 35? 3. What is the inequality that is repre- sented by the graph? A. y 7 B. y 7 –5 –4 –3 –2 –1 0 1 2 3 4 5 C. y 7 D. y 7 A. x 3 B. 3 x 4 C. x 4 D. 3 x 4 9. The solution to n 6 7 2 is 4 4. Which graph represents the inequality A. n 2 B. n 56 x 1? C. n 16 D. n 16 A. 10. Which graph represents the solution to –3 –2 –1 0 1 2 3 3w 4 19? B. –3 –2 –1 0 1 2 3 A. –2 –1 0 1 2 3 4 5 6 C. –3 –2 –1 0 1 2 3 B. –7 –6 –5 –4 –3 –2 –1 0 1 D. –3 –2 –1 0 1 2 3 C. –11 –10 –9 –8 –7 –6 –5 –4 –3 5. Which graph represents the inequality D. 3 x 2? –7 –6 –5 –4 –3 –2 –1 0 1 A. 11. For each inequality, tell whether the –4 –3 –2 –1 0 1 2 3 given value of the variable is a solution. B. a. x 8 15; x 4 –4 –3 –2 –1 0 1 2 3 b. 6x 30; x 8 C. –4 –3 –2 –1 0 1 2 3 c. 4y 7 12; y 1 D. d. 2z 2 4; z 2 –4 –3 –2 –1 0 1 2 3160 Chapter 5 • Writing and Solving Equations
- 23. 12. Solve each inequality and graph its so- 17. The Drama Club wants to collect at lution. least $1,500 from their performance of A Raisin in the Sun. They estimate that a. 2x 12 they will sell 400 tickets. How much b. y 5 2 should they charge for tickets? c. x 1 18. The greatest load that a freight elevator 4 d. z 3 4 can carry is 2,000 pounds. Ricky has cartons of paper that each weigh 4013. Solve each inequality and graph its so- pounds. Ricky must ride with the car- lution. tons, and he weighs 140 pounds. What a. 4x 5 17 is the greatest number of cartons Ricky b. 2y 3 11 can safely transport at one time? c. n 2 3 19. When 26 is subtracted from 3 times a 5 d. 3w 7 2 number, the result is greater than 10. What numbers are possible?14. What integers belong to the graph of 20. a. Mr. Lopez must drive 340 miles to 4 x 6? attend an origami convention. His15. Describe the solution of x 1 x. car averages 28 miles per gallon and so far he has traveled 102 miles. How much gasoline must be left inConstructed-Response his tank if he wants to complete theQuestions trip without stopping? b. At the convention, Mr. Lopez madeFor problems 16–19: origami swans, cranes, and dragons.a. Assign a variable to the unknown quan- He made three times as many swans tity. as cranes. He made five more cranesb. Write an inequality you can use to find than dragons. In all, he made 25 the unknown quantity. origami figures. How many of eachc. Solve the inequality. Show your work. did he make?16. Sasha needs to score at least 360 points on four tests to earn an A. On her first three tests she scored 86, 93, and 88. What must she score on the fourth test to earn an A? 5.8 Working with FormulasA formula is an equation that shows how two or more variables are re-lated to each other. Formulas are often used to represent scientific,business, or other real-life relationships. To evaluate a formula means to find the value of one of the variableswhen the values for the other variables are given. Working with Formulas 161
- 24. Model Problems 1. The distance formula d rt says that the distance an object travels is equal to the product of its rate of travel and the time it travels. How far does an airplane traveling at 550 miles per hour go in 3.5 hours? Solution Decide what values are given for the formula d rt. r 550 mph t 3.5 hours d rt d 550(3.5) d 1,925 miles Answer The plane travels a distance of 1,925 miles. 2. The formula for the Celsius temperature equivalent to a given Fahren- heit temperature is C 5 (F 32). What Celsius temperature is equiva- 9 lent to 95°F? Solution Substitute 95 as the value of F into the formula C 5 (F 32). 9 C 5 (95 32) Work inside the parentheses first. 9 C 5 (63) Multiply. 9 C 35 Answer A temperature of 35°C is equivalent to 95°F. 3. Moira’s salary is equal to $10.80 times the number of hours worked. a. Write a formula expressing the relationship between salary and hours worked. b. How much is Moira’s salary if she works 31 hours? Solution a. Let S represent salary and h represent hours worked. Salary $10.80(hours worked) S $10.80h b. Evaluate S $10.80h for h 31. S $10.80(31) $334.80 Answer Moira earns $334.80. Note: The next problem shows that sometimes it is convenient to rewrite a formula in terms of a different variable.162 Chapter 5 • Writing and Solving Equations
- 25. 4. The formula for the area of a rectangle is A lw (length times width). Find the width of a rectangle whose area is 204 square inches and whose length is 12 inches. Solution To get w by itself on one side of the equal sign, solve the for- mula for w like you would any equation. A lw w is multiplied by l. Use the inverse operation. A lw Divide both sides by l. l l A w or w A l l Substitute in the given values for A and l: w A 204 l 12 w 17 Answer The width is 17 inches. Practice1. Which formula is NOT equivalent to 4. Which formula expresses the relation- the others? ship between the cost C of a bag of bagels and the number of bagels n if A. d r t B. t r d each bagel costs $0.60? C. d rt D. r d t A. C $0.60n B. n $0.60C2. Use the formula C 5 (F 32). What C. C # n $0.60 9 Celsius temperature is equivalent to D. C $0.60 n 59°F? 5. Which formula expresses the relation- A. 15°C B. 48.6°C ship between x and y shown in the C. 15°C D. 55°C table? x 3 6 10 173. In chemistry, the formula P nRT is V y 1 4 8 15 used to find the pressure of a gas. Find P for n 10, R 50, T 12, and V 480. A. x y 2 B. y x 2 A. 1.1 B. 1.25 C. y 2x 5 C. 11.52 D. 12.5 D. x y 3 Working with Formulas 163
- 26. 6. Which formula expresses the relation- 13. s 16t2 64t h ship between y and m shown in the table? a. t 1, h 144 b. t 5, h 200 y 2 3.5 5 7 m 24 42 60 84 Constructed-Response A. y 12m Questions B. m y 20 C. m 12y 14. The formulas for converting Fahren- heit temperatures to Celsius and D. y 1 m 10 Celsius temperatures to Fahrenheit are 2 given below. Choose the correct for- 7. Use the formula d rt, where d dis- mula and find each temperature. Show tance, r rate, and t time. How long your work. would it take a car traveling 80 kilome- °C 5 (°F 32) ters per hour to travel a distance of 336 9 kilometers (if it made no stops)? 9 °C °F 32 A. 4.2 hours B. 4.8 hours 5 C. 5.6 hours D. 44.8 hours a. A temperature of 20°C corresponds 8. The formula C $1 $0.07(m 20) to what Fahrenheit temperature? gives the cost of a long-distance tele- b. A temperature of 50°F corresponds phone call of m minutes when m 20. to what Celsius temperature? Find the cost of a 35-minute call. For problems 15 and 16, write a formula A. $1.05 B. $2.05 that expresses the relationship between the C. $2.40 D. $3.45 variables in the table of values.Evaluate each formula for the given values 15. m 1 2.5 3.8 7of the variables. c 100 250 380 700 9. A r2 (Use 3.14.) a. r 5 16. x 0 2 5 8 b. r 30 y 1 5 11 1710. C P 0.06P a. P $50 17. A student’s score on a math test was b. P $120 determined by multiplying the number of correct answers (c) by 2.5, then11. P 2l 2w subtracting the number of incorrect a. l 26, w 19 answers (w). b. l 98.5, w 106.3 a. Write a formula for a student’s score12. I prt (S). b. Jasmine had 36 correct answers and a. p 2,000, r 0.07, t 3 4 incorrect answers. What was her b. p 8,500, r 0.06, t 4 score? c. Tony had 32 correct answers and 8 incorrect answers. What was his score?164 Chapter 5 • Writing and Solving Equations
- 27. 18. Write a formula for each relationship. 20. The formula C $8.00 0.45(h 15) gives the cost, C, of monthly Internet a. days and the number of hours in access for h hours a month when h them 15. Find C when h equals b. a car’s speed and its traveling time on a 280-mile trip a. 15 hours c. the total cost if admission is $5 and b. 26 hours each ride costs $2 c. 78 hours19. Use the formula I prt to write a for- mula for t. Chapter 5 Review 1. Which sentence means 16 is greater 7. Solve: x 2 5. than an unknown number plus 5? 4 A. 3 B. 12 A. 16 n 5 B. 5n 16 C. 18 D. 28 C. 16 n 5 D. 16 n 5 8. Evaluate the formula I prt when p 2. Which expression means the product of 3,000, r 0.05, and t 6. 4 and 3 less than a number? A. 1,800 B. 1,500 A. n 12 B. 4(n 3) C. 900 D. 90 C. 4(3 n) D. 12n 9. What is the inequality that is repre- 3. When x 6, the value of 5 3x is sented by the graph? A. 13 B. 2 –5 –4 –3 –2 –1 0 1 2 3 4 5 C. 8 D. 23 A. x 2 4. Evaluate 2g 4h 8k when g 10, B. 3 x 2 h 3, and k 1. C. 3 x 2 A. 26 B. 24 D. 3 x 2 C. 16 D. 0 10. How many integers are there that make 5. Which equation is paired with its solu- this statement true? tion? 5 x 4 A. x 5 18; x 23 A. 8 B. y 11 15; y 26 B. 9 C. 3z 42; z 13 C. 40 D. w 5 6; w 1 D. an infinite number 6. In 3 years, Joel will be 18. Which equa- 11. If m 20 and n 30, evaluate each ex- tion could be solved to find out how old pression. Joel is now? a. 80 15 m n b. 4(m n) A. a 3 18 B. 3a 18 C. a 3 18 D. a 18 3 Review 165
- 28. 12. Leo bought a radio for 3 of the original by 6. Subtract 19.” If Romare’s result 4 was 59, what was his original number? price. He paid $36. Show your work. a. Write an equation that can be used 18. Alonzo graphed the numbers shown in to find the original price. the box on a number line. Write an in- b. Solve and check the equation you equality that describes where on the wrote. number line all these numbers are lo-13. If x 5 17, what does 2x 3 equal? cated. Show your work. 1.11 1.56 2.40 2.85 3.49 3.83 2.39 2.73 4.00 2.18Constructed-Response 3.05 3.91 1.84 2.09 1.55Questions 1.00 2.95 1.79 2.36 3.2014. On the Budget Plan, the monthly cost 19. a. Use the distributive property to mul- of a health club membership is C $35 tiply 5(x 9). 4(v 5) where v is the number of vis- b. Using x 7, verify that both expres- its and v 5. Find the monthly cost for sions in part a are equivalent. each number of visits: c. Solve 5(x 9) 110. Show your a. 5 b. 9 c. 20 work. 20. Carla needs to buy some gas because15. Solve and check: x 6 2. her car’s tank is empty. Where she lives, 5 gasoline is selling for between $1.6016. Solve and graph the solution: 12x and $1.75 per gallon. If Carla spends 15 9. $14.00 on gas, how many gallons will17. Yukari said to Romare, “Think of a she get? Explain how you solved the number between 1 and 20. Multiply it problem. Chapter 5 Cumulative Review 1. What is the standard form of thirty-six 3. 449,183 547 million, twelve thousand, nine hundred A. 883 r 182 eight? B. 821 r 96 A. 3,612,908 C. 804 r 395 B. 360,012,980 D. 792 r 256 C. 36,120,098 4. What is the prime factorization of 80? D. 36,012,908 A. 4 4 5 2. Estimate 768 319. B. 22 4 5 A. 210,000 C. 24 5 B. 240,000 D. 25 5 C. 270,000 D. 320,000166 Chapter 5 • Writing and Solving Equations
- 29. 5. Baldwin had $40 to spend at the mall. 11. If 3x 10 1, find the value of each ex- He bought a CD for $11.99 and bought pression. lunch for $4.68. How much money did a. 6x 20 he have left? b. 5x 4 A. $23.33 12. Martina asked her boss for a salary of B. $24.43 $500 per week. She was offered a salary C. $22.15 of $19,500 per year. How much less was D. not enough information that than what she had requested? 6. 20.1 0.25 13. The areas of some large bodies of water A. 8.04 B. 8.4 are shown in the table. C. 80.4 D. 804 a. Round each area to the nearest 7. What part of the figure is shaded? thousand square miles. b. Write each rounded area in scien- tific notation. Area Rounded Scientific Name (sq mi) Area Notation Pacific Ocean 63,801,668 A. 1 B. 1 Caribbean 6 4 Sea 1,063,340 C. 1 D. 2 2 3 Gulf of Mexico 595,760 8. 9 1 42 4 3 A. 5 7 B. 4 7 Constructed-Response 12 12 Questions C. 5 5 D. 4 1 12 6 14. Buck said, “Gee whiz, there must be be- tween 10 and 20 animals in the yard!” 9. Multiply: 3 1 ( 20). 8 5 “Yes,” said Chuck. “There is one more cat than there are dogs, and there is A. 4 one more squirrel than there are cats.” 5 What is the greatest possible number of B. 3 dogs in the yard? Explain. 10 C. 6 15. A number is a common multiple of 7 D. 1 1 and 11. It is the least such number with 2 a sum of its digits equal to 11. Find the10. Solve: 0.2x 2 14. number. A. 2.4 B. 24 C. 60 D. 120 Cumulative Review 167
- 30. 16. Patty is a finance executive who works b. Write the expressions in order from in a skyscraper. On Thursday, she rode least to greatest value. up 17 floors from the floor where her 19. Henry bought four T-shirts, each the office is located to go to the Accounting same price. He gave the cashier $50.00 Department. Then she rode down 24 and received less than $3.00 change. floors to Human Resources. Finally, she rode down 19 floors to the Em- a. What is the least that one shirt could ployee Café on the 20th floor. On what cost? Show your work. number floor is Patty’s office? b. What is the most that one shirt could cost? Explain.17. a. Find 5 4 5 1. b. Show three different ways to change 20. Yvonne sewed a large square quilt the value of this expression using made up of 121 same-sized squares. parentheses. Find the value of each. The squares are alternately turquoise and magenta. How many turquoise and18. a. Find the value of each expression: how many magenta squares are there if (0.5)3, (0.4)2, (0.3)4. the corner squares are turquoise?168 Chapter 5 • Writing and Solving Equations

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