2017 AMC 10B Problems/Problem 12/section=4

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Solution 3

You can find that the ratio of fuel used by the old car and the new car in a same amount of distance is $3 : 2$, and the ratio between the fuel price of these two cars is $5 : 6$. Therefore, by multiplying these two ratios, we get that the costs of using these two cars is \[15 : 12 = 5 : 4\]So the percentage of money saved is $1 - \frac{5}{4} = \boxed{\textbf{(A)}\ 20\%}$.