AAPL wrote:GMAT Prep

If Mary always takes the same route to work, how long did it take Mary to get to work on Friday?

1) It took Mary 20 minutes to get to work on Thursday.
2) Mary's average speed on her trip to work was 25 percent greater on Thursday than it was on Friday.

OA C

Say the distance to work is d miles and speed on Friday was s miles per minute.

Thus, time taken to get to work on Friday = d/s minutes

Let's take each statement one by one.

1) It took Mary 20 minutes to get to work on Thursday.

Time taken to get to work on Thursday = d/s' = 20 minutes; here s' is the speed on Thursday

No information about the Friday. Insufficient.

2) Mary's average speed on her trip to work was 25 percent greater on Thursday than it was on Friday.

=> s' = 1.25*s => s = s'/1.25

Time taken to get to work on Friday = d/s = d/(s'/1.25) = 1.25*(d/s') = 1.25 * 20 = 25 minutes

Sufficient.

The correct answer: C

Hope this helps!

-Jay
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