DAILY GMAT BANK QUESTIONS PART 1

If a car travelled from Medan to Kisaran at an average speed of 40 mph and then returned to medan along the same route later that evening, what was the average speed for the entire trip?

(1) The trip from Medan to Kisaran took 50% longer than the trip from Kisaran to Medan.
(2) The route between Medan and Kisaran is 165 miles long.

ANSWER

(1) The trip from Medan to Kisaran took 50% longer than the trip from Kisaran to Medan.

Time from M to K 3/2 of that from K to M, thus
Speed from M to K 2/3 of that from K to M. Thus speed from K to M = 60 mph.

Now, , where d is the distance between K and M --> d reduces --> we can get the average time. Sufficient.

(2) The route between Medan and Kisaran is 165 miles long. We know nothing about the speed from K to M. Not sufficient.

Answer: A.