The idea is to place the nine numbers in the square in such a way that each of the eight (three rows, three columns and two diagonals) grey totals is the same.

Click on a number to select it, then click another to swap them over.

Hint: What must the total be? Try to work this out by thinking about what the totals of all three rows must add to...

1 | 2 | 3 | 6 | |

4 | 5 | 6 | 15 | |

7 | 8 | 9 | 24 | |

15 | 12 | 15 | 18 | 15 |