Unit 4 Lesson 8 Percent Increase and Decrease with Equations

The gas tank in Dad’s car hold 12 gallons. The gas tank in Mom’s truck holds 50% more than that. How much gas does the truck’s tank hold?

1. Find the new percentage.

2. What is the original value or amount?

3. Multiply the original amount times the new percentage.(as a decimal).

A movie theater decreased the size of its popcorn bags by 20%. If the old bags held 15 cups of popcorn, how much do the new bags hold?

1. Find the new percentage.

2.What is the original amount?

3. Multiply the original amount by the percentage(as a decimal).

Compared to last year, the population of Boom Town has increased by 25%.  The population is now 6,600.  What was the population last year?

1. Find your new percentage.

2. Use a variable to represent the original amount since we do not know it.

3. We always multiply the percent by the original amount.

4. Set that equal to the new amount given to you in the equation.

After a 25% discount, the price of a t-shirt was $12.  

What was the price before the discount?

1. Find the new percentage.

2. We do not know the original price.

3. The percentage is always multiplied by the original price. We will use a variable in place of x.

4. Set your percentage and variable to be equal to your new amount.

After a 25% discount, the price of a t-shirt was $12.  

What was the price before the discount?

1. Find the new percent. (Is it a percent increase or decrease)

2. Find the new amount.

3. Divide the new amount by the percentage.