The tail of a 1-mile long train exits a tunnel exactly 3 minutes after the front of the train entered the tunnel. If the train is moving 60 miles per hour, how many miles long is the tunnel?

The tail of the train starts one mile from the mouth of the tunnel and it must travel that distance plus the length of the tunnel in 3 minutes.

Let t = tunnel length

t + 1 = distance the tail must travel in 3 minutes.

3 minutes = 1/20 hr

(t+1) miles / 60 m/hr = 1/20 hr

t + 1 = 60/20

t+1 = 3

Subtract 1 from each side:

t = 2

The tunnel is 2 miles long.

60 mph is One mile a minute. So the train will start to exit the tunnel after 7 minutes. It will finish exiting the tunnel 1.5 mins later.