Expert: Scott A Wilson - 2/18/2010

Question
Train A leaves a station at 40mph.  Two hours later, Train B leaves the same station traveling in the opposite direction at 60mph.  How long after Train B leaves the station will it take for them to be 230 miles apart?

Answer
Train A leaves at 40mph.  Two hours later, it has gone 80 miles.
Also, two hours later, B leaves in the opposite direction at 60 mph.

The distance between them is growing, since they are in opposite directions, at 40+60 = 100 mph.
When B leaves, the distance is already 80, so at some later time it is 80 + 100t,
in miles, with t in hours.

Setting 80 + 100t= 230 gives 100t = 150, or t = 1.5.
That is in hours, so t = 1 hour, 30 minutes.