Imagine you have a 5 x 5 grid. You have to place the numbers 1-25 on the grid so that each row, column and diagonal add up the the same number, can it be done?
For example, here's what I mean with a 3x3 version.
4 9 2
3 5 7
8 1 6
All columns, rows and diagonals all add up to 15.
I would love someone to work this out, been annoying me for ages.