Solution on Monday.
A shop sells chocolates for £1 each, and you can exchange 3 wrappers for 1 chocolate. If you start off with £15, how many chocolates can you buy?
I have produced an ebook containing 101 of the previous Friday Puzzles! It is called PUZZLED and is available for the Kindle (UK here and USA here) and on the iBookstore (UK here in the USA here). You can try 101 of the puzzles for free here.