M16-08

Official Solution:


If a bus took 6 hours to travel from town A to town B, what was its average speed for the entire trip?

(1) In the first 2 hours, the bus covered a distance of 150 miles.

This information provides the average speed of the bus for the first 150 miles, which was 75 miles per hour. However, we don't know its average speed for the remaining 4 hours of the journey. Not sufficient.

(2) The average speed of the bus for the first half of the distance was twice its average speed for the second half of the distance.

This statement implies that the bus covered the first half of the distance in half the time it took to cover the second half of the distance. Since the journey took a total of 6 hours, the bus took 2 hours to cover the first half of the distance and 4 hours to cover the second half of the distance. Not sufficient.

(1)+(2) From (1), we know that in the first 2 hours, the bus covered a distance of 150 miles. From (2), we know that it took the bus 2 hours to cover the first half of the distance. Consequently, the entire journey was 300 miles long. As it took 6 hours to cover this distance, the average speed for the entire trip was 300/6 = 50 miles per hour. Sufficient.


Answer: C