Alan, Beti, Carol and Dai come to a river in the night.
There is a narrow bridge, but it can only hold two people at a time.
They have one torch and, because it's night, the torch must be used when crossing the bridge.
The torch will only last for 15 minutes.
Alan can cross the bridge in 1 minute, Beti in 2 minutes, Carol in 5 minutes, and Dai in 8 minutes.
When two people cross the bridge together, they must move at the slower person's pace.
How can they all cross within the time?
Well done to Mallory. First to send a correct solution although we have had some very inventive solutions!