Arrange three $1$s, three $2$s and three $3$s in this square so that every row, column and diagonal adds to the same total.
You might like to use this interactivity to do this problem.
You may like to try this with other sets of three consecutive numbers (numbers which come one after the other).
This problem has been adapted from the book "Numbers in Your Head" by John Spooner, published by BEAM Education. This book is out of print but can still be found on Amazon.