Sunday Times Teaser 2813 – Katy’s Piggy Banks

by Bob Walker

Published: 21 August 2016 (link)

Our granddaughter Katy has two piggy banks containing a mixture of 10p and 50p coins, making a grand total of £10. The first piggy bank contains less than the other, and in it the number of 50p coins is a multiple of the number of 10p coins.

Katy chose a coin at random from the first piggy bank and then put it in the second. Then she chose a coin at random from the second and put it in the first. She ended up with the same amount of money in the first piggy bank as when she started. In fact there was a 50:50 chance of this happening.

How much did she end up with in the first piggy bank?