Train Speed

[MAXWELL]

A man was quarter way through a tunnel when he heard a train coming If he ran back at 12mph he would out of the tunnel before the train entered.If he ran the other way at the same speed he would also be out of the tunnel before the train caught him. How fast was the train travelling

[spacechimp]

1 inch per second.

[Gnu]

18mph!

[Salty]

Assuming the man only just escapes at each end, then the train must be half a tunnel length away from the start of the tunnel and travelling at 24 mph.

If the man runs towards the train, he travels a quarter of the tunnel length at 12 mph, and the train travels twice that distance at 24 mph. They meet at the entrance.

If the man runs on through the tunnel, he runs three-quarters of a tunnel length at 12 mph and the train travels one and a half tunnel lengths at 24 mph. They meet at the exit.

[sddsddean]

Agree with salty, 24 mph (but I did it by algebra)

[Gnu]

Salty and sddsddean are quite right. I made some arithmetical error then realised my mistake once I'd gone to bed!

Salty's explanation is the simplest way of justifying the answer.

[MAXWELL]

Thanks for all the answers,yes it turned out to be 24mph. Wish I had payed more attention during Algebra lessons at school