Question

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 long is the tunnel? Hint : How far does the front of the train move in 3 minutes?

Answer 1

2 miles long

Step-by-step :

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.

Answer 2

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 long is the tunnel? Hint : How far does the front of the train move in 3 minutes?

Explanation

The front of the train moves 3 miles in 3 minutes. Therefore, the tunnel must be 1 mile long.