Sep 16, 2023
This puzzler is mathematical in nature. It is not automotive, but it does involve a train.
Two children are walking along a railroad track. (Don't try this at home people...)
It is a single railroad track. They enter a tunnel and they begin walking along the single track inside the tunnel. A very dangerous thing to do.
When they get to the point that is 2/5ths of the way into the tunnel, they hear the train coming behind them. They hear the train whistle.
There is no escape or exit, other than the beginning or the end of the tunnel. One the children begin running toward the train, back the way they came. They were only 2/5ths of the way in, so he goes that way. The other kid runs towards the end of the tunnel, the other 3/5ths of the way, away from the train.
They are both running at 15 miles per hour. So one kid runs toward the train. The other kid runs away from the train. And they just make it.
The puzzler is, how fast was the train going?
Now, you'll notice I left out some key pieces of information. How long is the tunnel? How far away is the train? You don't have that info.
Good luck.
Okay, the train tracks!
Kids in a tunnel. Walking along the track. They hear a train whistle behind them. They both start running, one in each direction. They are running at 15 miles per hour. How fast is the train going? And note, we left out how long the tunnel was and where the train was when they heard the whistle... Both of these are irrelevant.
Here is the answer.
It doesn't matter how long the tunnel is, or how long the train is. You can make the tunnel however long you want. It is the fractions that are important.
The truth is if you make the tunnel a mile, and the kid was running away from the train gets to the point that's four fifths of the way through the tunnel before the train enters the tunnel. So in order for this thing to work for him to get to the end of the tunnel when the train does, he must travel a fifth of a mile in the time it takes for the train to travel a whole mile, five fifths of a mile. So obviously he's going at 1/5 the speed of the train.
And we already told he's running 15 miles an hour so the train must be going at 75 miles an hour.
Simple. Cute.
