Lesson 15Finding This Percent of That

Learning Goal

Let’s solve percentage problems like a pro.

Learning Targets

  • I can solve different problems like “What is 40% of 60?” by dividing and multiplying.

Lesson Terms

  • percentage

Warm Up: Number Talk: Decimals

Problem 1

Find the value of each expression mentally.

Activity 1: Audience Size

Problem 1

A school held several evening activities last month—a music concert, a basketball game, a drama play, and literacy night. The music concert was attended by 250 people. How many people came to each of the other activities?

  1. Attendance at a basketball game was 30% of attendance at the concert.

  2. Attendance at the drama play was 140% of attendance at the concert.

  3. Attendance at literacy night was 44% of attendance at the concert.

Are you ready for more?

Problem 1

50% of the people who attended the drama play also attended the music concert. What percentage of the people who attended the music concert also attended the drama play?

Activity 2: Everything Is On Sale

Problem 1

During a sale, every item in a store is 80% of its regular price.

  1. If the regular price of a T-shirt is $10, what is its sale price?

  2. The regular prices of five items are shown here. Find the sale price of each item.

    item 1

    item 2

    item 3

    item 4

    item 5

    regular price

    sale price

  3. You found 80% of many values. Was there a process you repeated over and over to find the sale prices? If so, describe it.

    A tape diagram with a segment labeled 100% and a yellow part of it labeled 80%. A same size segment below has the same yellow portion labeled with a "?" and the entire diagram with an "x".

  4. Select all the expressions that could be used to find 80% of . Be prepared to explain your reasoning.

Lesson Summary

To find 49% of a number, we can multiply the number by or 0.49.

A tape diagram with 2 segments. The first segment is yellow. The top diagram is labeled 100% and the bottom is x. The top yellow segment is 49% while the bottom is 0.49x.

To find 135% of a number, we can multiply the number by or 1.35.

To find 6% of a number, we can multiply the number by or 0.06.

A triple number line with 5 tick marks. For the top number line, starting with the first tick mark, the numbers 0, the fraction 6 over 100, end fraction, times x, the fraction 49 over 100, end fraction, times x, x, and the fraction 135 over 100, end fraction, times x, are labeled. For the middle number line, starting with the first tick mark, the numbers 0, 0 point 0 6, times x, 0 point 4 9, times x, x, and 1 point 3 5, times x are labeled. For the bottom number line, starting with the first tick mark, the numbers 0, 6 percent, 49 percent, 100 percent, and 135 percent are labeled.

In general, to find of , we can multiply: