Adam and Beth each drove from Smallville to Crown City by different ro

Hi All,

This question can be solved with a mix of arithmetic and TESTing THE ANSWERS.

We're told that Adam drove 40 mph for 30 minutes. That distance = (40 mph)(1/2 hour) = 20 miles. We're then told that Beth's trip was 5 miles LONGER and 20 minutes MORE to complete - so she traveled for 25 miles and drove for 50 minutes. We're asked for Beth's average speed.

Beth drove for ALMOST an hour; if she had driven for an hour, then she would have an average speed of 25 mph. Since she drove that distance in a little LESS than an hour though, she would have driven a little faster than 25 mph.

Let's TEST Answer B: 30 mph

If she drove 30 mph for 50 minutes, then the total distance traveled would have been (30 mph)(5/6 hour) = 150/6 = 25 miles. This is an exact match for what we were told, so this MUST be the answer.

Final Answer:

GMAT assassins aren't born, they're made,
Rich

Since Adam drove 30 minutes, or 1/2 hour, at an average speed of 40 mph, he drove 1/2 x 40 = 20 miles. Since Beth’s route was 5 miles longer, she drove 25 miles. She also drove 20 minutes longer than Adam, so she drove for 50 minutes, or 5/6 hour. Thus, her average speed was

25/(5/6) = 25 x 6/5 = 30 mph

Answer: B

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