THE EIGHTEEN DOMINOES

The illustration shows eighteen dominoes arranged in the form of a square so that the pips in every one of the six columns, six rows, and two long diagonals add up `13`. This is the smallest summation possible with any selection of dominoes from an ordinary box of twenty-eight. The greatest possible summation is `23`, and a solution for this number may be easily obtained by substituting for every number its complement to `6`. Thus for every blank substitute a `6`, for every `1` a `5`, for every `2` a `4`, for `3` a `3`, for `4` a `2`, for `5` a `1`, and for `6` a blank. But the puzzle is to make a selection of eighteen dominoes and arrange them (in exactly the form shown) so that the summations shall be `18` in all the fourteen directions mentioned.