BTGmoderatorLU wrote:Source: GMAT Prep

Jane walked for 4 miles. What was her average speed for the first 2 miles?

1) Jane's average speed for the 4 miles was 3.2 miles per hour.
2) It took Jane 15 minutes longer to walk the second 2 miles than it took her to walk the first 2 miles.

The OA is C

Let's take each statement one by one.

1) Jane's average speed for the 4 miles was 3.2 miles per hour.

No information about the first 2 miles and the second 2 miles. Insufficient.

2) It took Jane 15 minutes longer to walk the second 2 miles than it took her to walk the first 2 miles.

Say time taken by Jane for the first 2 miles is x hours; thus, the time taken by her for the second 2 miles = x + 15/60 = (x + 0.25) hours

Thus, average speed = 4/(x + x + 0.25)

Since we do not know the average speed, we can't get the answer. Insufficient.

(1) and (2) together

average speed = 4/(x + x + 0.25) = 3.2

=> x = 0.5 hours

Jane's average speed for the first 2 miles = 2/0.5 = 4 mph. Sufficient.

The correct answer: C

Hope this helps!

-Jay
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