The simpler solution:
Step 0: Ignore the fly!
Step 1: The two trains are moving together at a speed of sL + sR, and so it will take d0 / (sL + sR) hours to meet.
Step 2: In that time the fly will have traveled sF x d0 / (sL + sR)
In the particular case: The engines are 60 miles apart, approaching each other at 60 mph (each is traveling at 30 mph), so they will meet in 1 hour. In that time the fly will have flown 60 miles!
Last updated 2002/05/30
© J.A.N. Lee, 2002.