Speed

crackgmat007 wrote:It took the bus 4 hours to get from town A to town B. What was the average speed of the bus for the trip?

1. In the first 2 hours the bus covered 100 miles
2. The average speed of the bus for the first half of the distance was twice its speed for the second half

In order to solve the problem you need to know how far the trip was so you can calculate the average speed based on the 4 hour trip.

Statement 1 is definitely not sufficient since it only tells you the average speed (50mph) for the first half of the trip. There is no information about how far the second half of the trip is. It could be another 100 miles or it could be 10 miles.

Statement 2 I believe is insufficient also because you still have two unknowns and only one equation. You do not know the total distance or either of the rates.

Even with both statements together, I do not believe you can solve this. Therefore, I believe the correct answer is E.

Taking both statements you have the time it took to cover 100 miles, 2 hours. In the second statement it gives you the rates for each half of the DISTANCE, but Statement one never says that 100 miles is the first half of the distance only that it took half the time. Therefore, the 100 miles could be 90% of the distance or 20% of the distance, it is still unknown.

If the prompt for statement 1 said that in the first 2 hours the bus covered half the distance, 100 miles. then you could solve it using both statements, or if either of the statements gave the total distance.

I hope that answer is correct, and if so hopefully I explained it clearly enough.