An ad for steel-belted radial tiers promises 18% better gas mileage. Tom's SUV has gotten 20.5 miles per gallon in the past.

Question

what mileage can he expect after the new tire installed

Answer 1

The answer is 24.2 mpg. Calculate it by starting with the original, and adding .18 times the original (18 percent). You will have 20.5 + .18(20.5) = 20.5 + 3.7 = 24.2 mpg

Answer 2

18% better means the new mileage is 1.18 times the old mileage. Do you understand why?