Anyone should be able to make a start on any of these resources. They are our favourites because they really get you thinking mathematically. There is a lot to explore in each one and we dare you to get as far as you can with every one. There are some that involve numbers and some that involve shapes. Some explore thinking strategically to win the game or solve the problem. Some lead on to proving important mathematical problems and some parts of some of them haven't yet been proved by even the best mathematicians.