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# Solving percent equations

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### Transcript

• 1. Percent Equations
September 1, 2010
• 2. A percent can tell you about the significance of a quantity.
The humane society found homes for 6 more puppies this month than last month.
Is this a big change?
If I was told this was a 100% increase over last month, the answer is yes.
If this is a 1% increase over last month, then the increase of 6 puppies is not much of a difference.
Why do we need percents
• 3. A percent can make it easier to compare quantities.
I could say that I scored a 18/25 on Quiz 1 and a 30/40 on Quiz 2.
If I use percents rather than fractions, the comparison would be more obvious: I scored a 72% on Quiz 1 and a 75% on Quiz 2.
Why do we need percents?
• 4. Grades
Weather Forecast
Chance of precipitation
Nutritional Labels
Download Status
Shopping
Sales Tax
Discounts
When do we see percents?
• 5. Percent literally means “per hundred.”
A percent is like a ratio because it compares a number to 100.
Understanding Percent
• 6. Decode the question into an equation.
Change percent to decimal.
Solve the equation.
Solving Percent Equations
• 7. What is 20% of 60?
What is 5% of 120?
Solving Percent Equations
x
=
0.20

60
X = 12
x
=
0.06

120
X = 6
• 8. You are reading a book. You have read 60% of the book. It has 700 pages. How many pages have you read?
What is 60% of 700?
Book Problem
x
=
0.60

700
X = 420 pages
• 9. 12% of what is 21?
40% of what is 90?
Solving Percent Equations
x
=
0.12

21
.12
.12
x = 175
=
0.4

90
x
.4
.4
x = 225
• 10. 7 students in Algebra 1 have A’s. They make up 25% of the class. How many students are in the class?
25% of what is 7?
Students in a class
x
=
0.25

7
.25
.25
X = 28
• 11. What percent of 330 is 21?
What percent of 30 is 48?
Solving Percent Equations
X

330
=
21
330
330
x = 0.065 ≈6.4%
X

30
=
48
30
30
x = 1.6 = 160%
• 12. Six students make an F on the exam on Friday. There are 27 students in the class. What percentage of students failed the exam?
What percent of 27 is 6?
Solving Percent Equations
X

27
=
6
27
27
x = 0.22 ≈ 22.2%
• 13. 18% of what number is 9?
What percentage of 200 is 40?
45 is what percent of 54?
Exit Slip