Three people chose this as a favourite problem. It is the sort of problem that needs thinking time - but once the connection is made it gives access to many similar ideas.
Libby Jared helped to set up NRICH and this is one of her favourite problems. It's a problem suitable for a wide age range and best tackled practically.
Lyndon chose this as one of his favourite problems. It is accessible but needs some careful analysis of what is included and what is not. A systematic approach is really helpful.
There are many different methods to solve this geometrical problem - how many can you find?
A new problem posed by Lyndon Baker who has devised many NRICH problems over the years.
Nick Lord says "This problem encapsulates for me the best features of the NRICH collection."