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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