Lesson 6Increasing and Decreasing
Learning Goal
Let’s use percentages to describe increases and decreases.
Learning Targets
I can draw a tape diagram that represents a percent increase or decrease.
When I know a starting amount and the percent increase or decrease, I can find the new amount.
Lesson Terms
- percentage decrease
- percentage increase
Warm Up: Improving Their Game
Problem 1
Here are the scores from 3 different sports teams from their last 2 games.
sports team | total points in game 1 | total points in game 2 |
---|---|---|
football team | ||
basketball team | ||
baseball team |
What do you notice about the teams’ scores? What do you wonder?
Which team improved the most? Explain your reasoning.
Activity 1: More Cereal and a Discounted Shirt
Problem 1
A cereal box says that now it contains 20% more. Originally, it came with 18.5 ounces of cereal. How much cereal does the box come with now?
Problem 2
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?
Activity 2: Using Tape Diagrams
Problem 1
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.
Problem 2
Draw a diagram to represent these situations.
The number of ducks living at the pond increased by 40%.
The number of mosquitoes decreased by 80%.
Are you ready for more?
Problem 1
What could it mean to say there is a 100% decrease in a quantity? Give an example of a quantity where this makes sense.
Activity 3: Agree or Disagree: Percentages
Problem 1
Do you agree or disagree with each statement? Explain your reasoning.
Employee A gets a pay raise of 50%. Employee B gets a pay raise of 45%. So Employee A gets the bigger pay raise.
Shirts are on sale for 20% off. You buy two of them. As you pay, the cashier says, “20% off of each shirt means 40% off of the total price.”
Lesson Summary
Imagine that it takes Andre
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,