Math CentralQuandaries & Queries


Question from Mary, a student:

A train, whose speed is 75 mph, takes 3 minutes to pass a car that is going 60 mph in the same direction. How long is the train?

Hi Mary.

Think about things in relation to one another.

If the train and car are going in the same direction, the difference in their ground speed is the relative speed between the two vehicles. That means the relative speed is 75 - 60 = 15 mph.

So how far can you go in 3 minutes when travelling at 15 mph?

Hope this helps,
Stephen La Rocque

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