If train A leaves Chicago traveling 100MPH and train B leaves New York traveling 150MPH and the distance between the two cites is 600 miles how far from New York will it be when the two trains meet?
360 miles from New York, that's trivial.
Train A, at two hours, will be 300
Train B, at two hours, will be 200
this leaves a remainder of 100 to be covered.
With a simple factoring ratio of 300/200, into the equation of the remaining 100 miles. this would factor into 60/40.
So, with the 300 already covered and the (now easily attained) other 60 miles into the equation, they would meet at exactly 360 miles. (A surprisingly easy number, considering these problems typically take much more work than simple factoring.)
Edit: Added the explanation for potential trolling baddies.