Question 37569
Since we are considering their distance relative to each other, we can consider this problem this way...
Noah runs 2 mph faster than Ben.  Imagine Ben standing still and Noah is running away from him at 2 mph.  
Now distance = rate x time.
We need to find the time it takes to cover 1/3 of a mile at a rate of 2 mph.
So we have
D = RT
1/3 = 2T
T = 1/6 hour or 10 minutes