train A and B

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train A and B

by j_shreyans » Fri Sep 26, 2014 10:18 am
While on straight, parallel tracks, train A and train B are traveling at different constant rates. If train A is currently 2 miles behind train B, how many minutes from now will train A be 4 miles behind train B?

(1) Three minutes ago, train A was 1 mile behind train B.

(2) Train A is traveling at 80 miles per hour, and train B is traveling at 100 miles per hour.

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by GMATGuruNY » Fri Sep 26, 2014 10:33 am
j_shreyans wrote:While on straight, parallel tracks, train A and train B are traveling at different constant rates. If train A is currently 2 miles behind train B, how many minutes from now will train A be 4 miles behind train B?

(1) Three minutes ago, train A was 1 mile behind train B.

(2) Train A is traveling at 80 miles per hour, and train B is traveling at 100 miles per hour.
Statement 1:
3 minutes ago, train B was 1 MILE AHEAD of train A.
Now -- 3 minutes LATER -- train B is 2 MILES AHEAD of train A.
Implication:
Every 3 minutes, train B pulls ahead of train A by 1 more mile.
Thus:
6 minutes from now, train B will pull ahead of train A by 2 more miles, with the result that train A will be 4 miles behind train B.
SUFFICIENT.

Statement 2:
Since the speed of each train is known, we can determine how long it will take train A to be 4 miles behind train B.
SUFFICIENT.

The correct answer is D.
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