Grade 7 Proportions: Percent Change

Worked examples

Real problems from the practice worksheets, solved one step at a time.

1. Example 1

   The price of a bike dropped from $40 to $20. What is the percent decrease?

   1. Find the amount of change: 40 − 20 = 20.
   2. Compare it with the ORIGINAL amount (40): 20 ÷ 40 = 0.5.
   3. Write it as a percent: 0.5 × 100 = 50%.
   4. So the percent decrease is 50%.

   Answer: 50%

2. Example 2

   Maya estimated that a jar held 48 beans. The jar actually held 40 beans. What is the percent error of her estimate?

   1. Find how far off the estimate was: |48 − 40| = 8.
   2. Compare with the ACTUAL amount: 8 ÷ 40 = 0.2.
   3. Write it as a percent: 0.2 × 100 = 20%.
   4. So the percent error is 20%.

   Answer: 20%

3. Example 3

   An $88 scooter is on sale for 50% off. What is the sale price, in dollars?

   1. Find 50% of $88: 88 × 50 ÷ 100 = 4400 ÷ 100 = 44.
   2. It goes DOWN, so subtract: 88 − 44 = 44.
   3. Check: 50% of 88 is 88 × 0.5 = 44.
   4. So the sale price is $44.

   Answer: 44