Percent Increase and Decrease

Percent Increase and Decrease

Definitions

• Percent Change--the percent by which a number increases or decreases.

• Percent Increase--the percent change that describes an increase in a quantity

• Percent Decrease--the percent change that describes an decrease in a quantity

Percent Change Proportion

We can solve for the percent change using the proportion at the right.

How is this proportion similar to the proportion we used yesterday?

How is it different?

Multiple Choice

Which of the follow proportions could be used to find the percent that Amber's wage increase?

Remember:

 $\frac{amount\ of\ change}{original\ amount}=\frac{\%}{100}$  

•  $\frac{8}{10}=\frac{x}{100}$  

•  $\frac{2}{10}=\frac{x}{100}$  

•  $\frac{2}{8}=\frac{x}{100}$  

•  $\frac{10}{8}=\frac{x}{100}$  

Multiple Choice

What percent did Amber's wage increase?

Remember: 
 $\frac{2}{8}=\frac{x}{100}$  can be used to find the percent increase.

• 25%

• 4%

• 50%

• 400%

Multiple Choice

Which of the following proportions could be used to find the percent that Alex's grade decreased?

• $\frac{8}{72}=\frac{x}{100}$

• $\frac{72}{80}=\frac{x}{100}$

• $\frac{8}{100}=\frac{x}{80}$

• $\frac{8}{80}=\frac{x}{100}$

Multiple Choice

By what percent did Alex's math grade decrease?

Remember:

 $\frac{8}{80}=\frac{x}{100}$  

• 80%

• 10%

• 1,000%

• 64%

Poll

How are you feeling about solving percent increase and decrease problems?

• I feel great! I can do these problems on my own.

• I am doing ok. I still need some more practice.

• I have no clue how to do these problems.

Multiple Choice

You decide to go see a movie with your friends over Thanksgiving Break. If you buy the ticket before noon, the price is $5. However, if you purchase the ticket after noon, the price increase to $8. By what percentage did the price increase?

• 55%

• 95%

• 60%

• 160%

Multiple Choice

Yesterday, Mrs. Dusterhoft had 70 tests to grade. Today she has 21 tests to grade. By what percentage did the number of tests she has to grade decrease?

• 60%

• 70%

• 30%

• 231%

Multiple Choice

Ms. Hall needs a new pair of climbing shoes. She found a pair at Academy that originally cost $80. The shoes are on sale for $68. By what percentage was the price of the shoes decreased?

• 12%

• 15%

• 32%

• 10%

Multiple Choice

There were 28 students in the chess club. If the number of students in the chess club increased by 50%, how many new students are in the chess club?

• 28

• 50

• 20

• 14

Multiple Choice

Challenge Problem: Nathan usually drinks 40 ounces of water a day. He read that he should drink 50% of his body weight (ie, 50 lbs = 50 oz of water). If Nathan weighs 128 pounds, by what percentage does he need to increase the number of ounces of water he drinks?

• 60%

• 50%

• 160%

• 64%

Great job!

Now you can calculate percent change.