The price per gallon of gasoline changes off the most drivers pay close attention to the changes find the percent changes in price for each of these cases increased from $4 per gallon to $4.20

4 + 4x = 4.20
.2 = 4x
.2/4 = x
x = 1/20 = .05 = 5%

Since it went up .20 we are looking for the percentage .20 is out of 4. since .20 is 20% out of 1, divide 20 by 4 to find the new percent which is 5%. therefore the gas prices increased 5%, and the new price is 105% of the original price.