Percents: Percent Change

The price of a gallon of gasoline was $30 on the 15th of March. By the 15th of April, the price per gallon had increased by 20%, and by the 15th of May the price had increased again to a total of $45 per gallon. What was the percent change in the price of a gallon of gasoline between the 15th of April and the 15th May?

Incorrect. Did you reach this answer by using the percent change formula?

Next, find the difference between the price in April and in May. >$$\$45 - \$36 = \$9$$ Now, use the percent change formula in order to calculate the percent increase. Remember, since the question describes a percent increase, the original is the smaller number (in this case, $36): >$$\text{Percent change} = \frac{9}{36}\cdot100 = \frac{1}{4}\cdot100 = 25\%$$

Incorrect. [[snippet]] Carefully check your calculations.

Incorrect. [[snippet]] Carefully check your work.

Incorrect. Note that the question refers to the percent change between April and May, and not between March and May. Slow down, score more—read the question carefully!

Good. Then you've noticed this is a percent change question and chosen the right tool for the job. However, you forgot that since the question refers to a percent increase, the original should be the smaller number. Use 36 as the denominator, not 45.

[[snippet]]

Looks like someone needs a refresher. The question uses the words _percent change_, therefore this is a percent change question. Use the percent change formula: $$\displaystyle \text{Percent change} = \frac{\text{Difference}}{\text{Original}} \cdot 100$$ In order to find the difference between the price in April and the price in May, first calculate the price in April.

Correct. [[snippet]] The price in April is 20% greater than in March, therefore: >$$\text{Price in April} = 30+\frac{20}{100}\cdot30$$ >>>>$$= 30+\frac{1}{5}\cdot30$$ >>>>$$ = 30+6$$ >>>>$$ = \$36$$

20%

25%

30%

35%

50%

Yes.

No.

The what formula?

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