This is a nice little investigation for children who are familiar with the layout for standard written addition. For this investigation you need a set of 0 - 9 cards. The task is to use any six of the cards to make the blank sum correct. Only one number can go in each box. With some logical thinking children should realise that for the answer to be in the hundreds then the tens digit has to be a 9. Also the hundreds digit of the answer has to be 1. (There may be some pupils who use a zero in the hundreds - use this as a discussion point). Working on from this, the zero has to go in the tens column of the answer. This leaves these possibilities: Finding one answer may be quite easy but the task is to find all the possibilities and will require working in a well organised systematic way. Go to year 4 Challenge: Crazy Addition