Unit 4 Lesson 8 Percent Increase and Decrease with Equations

Unit 4 Lesson 8 Percent Increase and Decrease with Equations

Writing an Percent increase as an Equation when given the original amount.

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).

Multiple Choice

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?

• 150(12)

• 1.50(12)

• 50(12)

• .5(12)

Writing a Percent decrease as an equation when given the original amount.

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).

Multiple Choice

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?

• 0.20(15)

• 1.20(15)

• 0.80(15)

• 80(15)

Writing a Percent increase as a equation when given the new amount.

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.

Multiple Choice

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?

• 1.25x=6,600

• 1.25(6,600)

• 0.25x=6,600

• 0.75x=6,600

Writing a percent decrease as an equation when given the 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 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.

Multiple Choice

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

What was the price before the discount?

• 0.25(12)

• 0.25x=12

• 0.75(12)

• 0.75x=12

Multiple Choice

Compared to last year the price of Netflix has gone up by 15%. The subscription is now $16. What is the equation to solve for last year's price?

• 1.15x=16

• 0.15(16)

• 0.15x=16

• 1.15(16)

Solving for a percent increase or decrease when only given the new amount/value.

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.

Multiple Choice

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

What was the price before the discount?

• 16

• 14

• 11

• 18

Multiple Choice

Compared to last year the Chiefs are scoring 9% more touch downs. This year they are scoring 5 touch downs. How many touch downs were the Chiefs scoring last year?

• 3

• 4.6

• 0.5

• 5.45