On a recent trip, Cindy drove her car 290 miles, rounded to the nearest 10 miles, and used 12 gallons of gasoline, rounded to the nearest gallon. The actual number of miles per gallon that Cindy’s car got on this trip must have been between

A. 290/12.5 and 290/11.5

B. 295/12 and 285/11.5

C. 285/12 and 295/12

D. 285/12.5 and 295/11.5

E. 295/12.5 and 285/11.5

**Correct Answer:** D

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You’ll find tons of practice questions, explanations for GMAT Official Guide questions, and strategies on our GMAT Question of the Day page.

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For which of the following functions is f(a+b) = f(b) + f(a) for all positive numbers a and b?

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This is one of the most difficult questions in the GMAT universe. That said, there is a simple way to solve it that relies on a fundamental divisibility rule every GMAT studier should know:

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