Gas costs $2.53 per gallon in May. In September, gas cost $3.05 per gallon. What was the percent change in the cost of a gallon of gas?

First, find the difference:

$3.05 - $2.53

= $0.52

Take the positive difference and divide with the original price:

0.52 / 2.53

= 0.2055 (bunch of numbers)

Then, multiply that by 100 or move the decimal 2 places to the right.

20.55 (rounded)

Your answer is:

20.6%