The idea is to place the nine numbers in the square in such a way that each of the ten (four rows, four 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 the rows must add to...

1 | 2 | 3 | 4 | 10 | |

5 | 6 | 7 | 8 | 26 | |

9 | 10 | 11 | 12 | 42 | |

13 | 14 | 15 | 16 | 58 | |

34 | 28 | 32 | 36 | 40 | 34 |