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 Simple trains problem (Posted on 2017-08-29)
A freight train going in one direction takes 3 minutes to pass a crossing. A slower train of the same length on a parallel track in the other direction takes 4 minutes.

How long does it take these trains to pass each other?

 No Solution Yet Submitted by Jer Rating: 3.0000 (1 votes)

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 Simple Solution (spoiler) | Comment 1 of 2
If they start head to head (on parallel tracks) then they will be alongside each other (head to foot, engine to caboose) when the faster train has traveled 4/7 of its length and the slower train has traveled 3/7 of its length.  This takes 3 minutes * 4/7 = 4 minutes * 3/7 = 12/7 minutes.  Double this to get the time at which they will have passed each other (caboose to caboose).

 Posted by Steve Herman on 2017-08-29 09:57:56

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