Walkabout wrote:

At what speed was a train traveling on a trip when it had completed half of the total distance of the trip?

(1) The trip was 460 miles long and took 4 hours to complete.

(2) The train traveled at an average rate of 115 miles per hour on the trip.

Solution:

We need to determine at what speed a train was traveling when it completed ½ of its trip.

Statement One Alone:The trip was 460 miles long and took 4 hours to complete.

With the information in statement one, we can determine the average speed of the train for the entire trip.

average speed = total distance/total time

average speed = 460/4

average speed = 115

Although we know that the train traveled at an average speed of 115 mph, we do not know whether the train traveled

at a constant rate. Thus, we cannot determine the speed of the train when it completed half of the total distance. Statement one alone is not sufficient to answer the question. We can eliminate answer choices A and D.

Statement Two Alone:The train traveled at an average rate of 115 miles per hour on the trip.

We see that statement two provides the same information as statement one and thus is also not sufficient to answer the question. We can eliminate answer choice B.

Statements One and Two Together:Since statements one and two provide identical information and are each insufficient, we know that the statements together are also insufficient.

The answer is E.

_________________

Jeffery Miller

Head of GMAT Instruction

GMAT Quant Self-Study Course

500+ lessons 3000+ practice problems 800+ HD solutions