Two trains, A and B, leave their respective starting points at the same time and travel in opposite directions. They travel at constant speeds, and pass at point M. One travels at twice the speed of the other. If one of the trains leaves five minutes late they pass at a point 2 miles from point M.

What is the speed of the slow train, in miles per hour?

Okay. If the fast train is delayed, then it's five minutes from the meeting point when the slow on reaches it. The slow one will go 2 miles toward the fast one (away from point M) and the fast one will go 4 miles (twice as far, because it's going twice as fast) in the same time. That means the fast train was six miles from point M, and could cover that six miles in 5 more minutes. 6 miles in 5 minutes is 72mph, so the slow train is going 36.

Just as a check, say the slow train was delayed. Fast train is at point M, and slow one is 5 minutes from there. Fast train advances 2 miles from point M while slow train advances 1 mile, so the slow train was 3 miles from point M. 3 miles in 5 minutes is 36mph, so the fast train is going 72mph.

Posted by Ryan on 2003-05-10 07:04:56