MTH 232

1
MTH 232

• Section 7.4
• Percent

2
Overview

• It is nearly impossible to live in todays
  society and not be aware of the notion of
  percent.
• For students in Grades K 2, the emphasis should
  be on the relationship between percents and
  common fractions (for example, 50 ½). These
  relationships can be modeled relatively easily.
• In Grades 3 and 4, students begin to explore the
  relationship between fractions, decimals, and
  percents.
• Finally, in Grades 5 and 6 students learn to
  solve percent problems (usually by the proportion
  method).

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A Percent Is A Ratio

• percent, when translated from the Latin per
  centum, means per hundred
• This application of ratio measures the relative
  size of a part (the percent) to a whole (100)

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Modeling Percents
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Percents and Decimals

• To change a percent to a decimal, drop the
  percent sign and move the decimal two places to
  the left.
• To change a decimal to a percent, move the
  decimal two places to the right and add a percent
  sign.

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Percents and Fractions

• To change a percent to a fraction
• Drop the percent sign and write the percent over
  100.
• Be prepared to simplify and/or reduce.
• To change a fraction to a percent
• First change the fraction to a decimal. Then
  change the decimal to a percent, or
• Set up a proportion.

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Three Basic Types of Percent Problems

• Calculating the Percentage of a Number
• Calculating a Number of Which a Given Number is a
  Given Percentage
• Calculating What Percentage One Number Is of
  Another
• These types of problems can all be solved by
  either an equation (with decimals) or a
  proportion (with diagram)

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Examples

1. Sarah and her friends go out to eat. The total
   bill is 55. How much money should they leave if
   they want to leave a 15 tip?
2. Bill took a test and scored 85. If he got 17
   questions right, how many questions were on the
   test?
3. Juan made 25 out of 30 free throws. Anna made 33
   out of 40 free throws. Who had the higher
   percentage?