The price per gallon of gasoline changes often. most drivers pay close attention to those changes. find the percent change in price for each of these cases.
a) increase from $4.00 per gallon to $4.20
b) increase from $3.00 per gallon to $3.75
c) decrease from $3.75 per gallon to $3.00

A) The amount of change is .20 (20 cents) so we need to find what percent of $4.00 is .20...
4 * x = .20
x = .20/4 = .05

Multiply by 100 (move decimal 2 places to the right) to change decimal to percent.

.05 = 5% increase

b)The increase is .75.  What percent of 3.00 is .75

3 * x = .75
x = .75/3
x = .25 x 100 = 25% increase

c) The amount of change is .75 but this time we are going from 3.75 to 3.00 so we find out what percent .75 is of 3.75.

3.75 * x = .75
x = .75/3.75
x = .20 x 100 = 20% decrease