Data Sufficiency

Hi!
Statement (2) means that, as they are travelling at constant rates, the distance between them will change with time. As they were 0.5 miles apart three minutes ago, and now they are 1 mile apart, we can predict that they will be:
- 1.5 miles apart in 3 minutes from now
- 2 miles apart in 6 minutes from now
Thus STATEMENT (2) IS SUFFICIENT.

Also STATEMENT (1) IS SUFFICIENT. The difference of speed between them is 10 miles per hour, which means that it will take 1/10 hour (6 minutes) for car X to be one more mile ahead of car Y.

The answer is (D).

While on a straight road, car X and car Y are traveling at different constant rates. If car X is now 1 mile ahead of car Y, how many minutes from now will car X be 2 miles ahead of car Y?

(1) Car X is traveling at 50 miles per hour and car Y is traveling at 40 miles per hour.
(2) 3 minutes ago car X was 1/2 mile ahead of car Y.

Target question: How many minutes from now will car X be 2 miles ahead of car Y?

Given: Car X is now 1 mile ahead of car Y

Statement 1: Car X is traveling at 50 miles per hour and car Y is traveling at 40 miles per hour.
Notice that we could easily duplicate this scenario in real life.
Start with Car X 1 mile ahead of car Y (given info)
Have Car X drive at 50 mph and car Y at 40mph.
Use a stopwatch to time how long it takes for Car X to be 2 miles ahead of Y.
As you can see, we have enough information to answer the target question
Since we can answer the target question with certainty, statement 1 is SUFFICIENT

Statement 2: 3 minutes ago car X was 1/2 mile ahead of car Y.
If car X is presently 1 mile ahead, we can see that car X gains 1/2 mile every 3 minutes.
At that rate, car X will gain another 1 mile in 6 minutes.
Since we can answer the target question with certainty, statement 2 is SUFFICIENT

Answer = D

Cheers,
Brent