Unit 4, Lesson 6
Increasing and Decreasing
Grade 7
6.2
Activity
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A shampoo bottle says that now it contains 20% more. Originally, it came with 18.5 fluid ounces of shampoo. How much shampoo does the bottle come with now?
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The price of a shirt is \$18.50, but you have a coupon that lowers the price by 20%. What is the price of the shirt after using the coupon?
6.3
Activity
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Match each situation to a diagram. Be prepared to explain your reasoning.
- Compared with last year’s strawberry harvest, this year’s strawberry harvest is a 25% increase.
- This year’s blueberry harvest is 75% of last year’s.
- Compared with last year, this year’s peach harvest decreased 25%.
- This year’s plum harvest is 125% of last year’s plum harvest.
A B -
Draw a diagram to represent these situations.
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The number of ducks living at the pond increased by 40%.
- The number of mosquitoes decreased by 80%.
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Student Lesson Summary
Imagine that it takes Andre more than the time it takes Jada to get to school. Then we know that Andre’s time is , or 1.75, times Jada’s time. We can also describe this in terms of percentages:
Two tape diagrams. Jada's time, 4 white equal sections, labeled 100 percent. Andre's time, 7 equal sections labeled 175 percent, 4 white and 3 blue.
We say that Andre’s time is 75% more than Jada’s time. We can also see that Andre’s time is 175% of Jada’s time. In general, the terms percent increase and percent decrease describe an increase or decrease in a quantity as a percentage of the starting amount.
For example, if there were 500 grams of cereal in the original package, then “20% more” means that 20% of 500 grams has been added to the initial amount, , so there are 600 grams of cereal in the new package.
We can see that the new amount is 120% of the initial amount because
Tape diagram. 6 equal sections, 1 shaded blue. 120 percent labels the entire tape. 100 percent labels 5 sections. 20 percent labels the one blue shaded section.
A percent decrease tells how much a quantity went down. It is written as a percentage of the starting amount.
For example, a store had 64 hats on Friday. It had 48 hats left on Saturday. The number of hats went down by 16.
This was a 25% decrease, because 16 is 25% of 64.
A percent increase tells how much a quantity went up. It is written as a percentage of the starting amount.
For example, Elena had \$50 in the bank on Monday. She had \$56 on Tuesday. The amount went up by \$6.
This was a 12% increase, because 6 is 12% of 50.