Four 4s

A classic problem from the 19th century that can used as an introduction to priority of operations (BIDMAS) and factorials. There are different ways on finding solutions, and it depends on what you allow to be used. Can also be used to help show the difference between binary operations (such as addition etc where two numbers are combined to make a single number) and unary operations (such as square root and factorial which are applied to a single number giving, in most cases, a different value).

An ActivInspire flipchart and a pdf file are both available with screens and links to other sources including an excellent Numberphile video which shows that if you choose the correct function then every number can be made – which takes the fun out of the problem, so we do not allow this!