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CALCULATING PERCENT INCREASE AND DECREASE
Jump right to the exercises!
When a quantity grows (gets bigger), then we can compute its PERCENT INCREASE:
PERCENT INCREASE = (new amount - original amount)/(original amount)
When a quantity shrinks (gets smaller), then we can compute its PERCENT DECREASE:
PERCENT DECREASE = (original amount - new amount)/(original amount)
Both formulas have the following pattern:
PERCENT INCREASE/DECREASE = (change in amount)/(original amount)
Notice that when you compute percent increase or decrease,
you always compare how much a quantity has changed to the original amount.
EXAMPLES:
Question: A price rose from $5 to $7. What percent increase is this?
Answer: Which is the original price? $5; this will be the denominator.
% increase = (7-5)/5 = 2/5 = 0.40 = 40%
Note: Be sure to give your answer as a PERCENT.
Question: A quantity decreased from 90 to 75. What percent decrease is this?
Answer: Which is the original quantity? 90; this will be the denominator.
% decrease = (90-75)/90 = 15/90, which is approximately equal to 16.67%
Note: If an answer does not come out exact, then round to two decimal places.
Question: An item went on sale for $13 from $16. What percent decrease is this?
Answer: Which is the original price? $16; this will be the denominator.
% decrease = (16-13)/16 = 0.1875 = 18.75%
On this exercise, you will not key in your answer.
However, you can check to see if your answer is correct.