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7th Grade Math / Lesson 2: Percents II

PERCENTS
What will we be learning in this lesson?


  • In this lesson, you will learn how to evaluate percents.

    Vocabulary words are found in this purple color throughout the lesson. Remember to put these in your notebook.


PERCENTS


  • Percents are used to help make comparisons. They compare quantities in terms of 100. The word "percent" actually means "per hundred".
  • There is a proportion to use when solving any type of percent problem.


  • Suppose you were going to pay 80% of the original price for a pair of jeans. The original price is $40. How much would you pay? To set up this proportion, 80 would be the percent number and 40 would be the "whole" because it is the original price. In this case, it is the "part" that you are looking for.
  • Let's look at how to solve this.


PERCENTS


  • First, put the numbers in where they belong.



  • Then, solve the proportion. Find the numbers on the diagonal that you know. There are two diagonals - the 40 and the 80 is one of them, and the "part" and the 100 is the other diagonal.

  • We will need to use the diagonal with the 40 and the 80 since we know both of the numbers. MULTIPLY these numbers together. 40 * 80 = 3200

  • Now take that answer and DIVIDE by the other number in the problem that has not been used yet. 3200 100 = 32.
    So the price that you will pay for the jeans is $32.


PERCENTS


  • Let's find another one. There are 40 students on the class roster. 75% of them passed the Achievement Tests. Find out how many students passed.

  • You need to figure out what you know and what you are looking for.
  • The problem says to "Find out how many students..." so the percent is NOT the number we are looking for. We need the number of students.

  • Do we need the total number of students? NO, only part of the number of students.

    So we have the percent value and the "whole" for the proportion.



PERCENTS


  • Now let's solve the proportion.

  • Find the diagonal of numbers that we know.


  • Multiply the numbers on this diagonal. 40 * 75 = 3000

  • Then divide by the other number that you haven't used yet.
    3000 100 = 30

    So the number of students that passed the Achievement Test is 30.


PERCENTS


    REMEMBER

  • Once you have your proportion set up, MULTIPLY the diagonal of numbers that you have, then DIVIDE by the number not used yet.


  • Can you set up the proportion to find a missing number in a percent problem?

  • Can you solve the proportion to find the missing number?

  • Be sure to go back to your classroom to get any homework assignments or other activities you need to attend to.