Make nine squares with twenty-four matches ([Fig. 12]). 62 Then request some one to remove eight matches, and without touching those left, to leave two perfect squares.
Fig. 12.
[Fig. 13] shows the solution.
Fig. 13.
YOUR OPPONENT MUST TAKE THE LAST MATCH
Place twenty-five matches in a row on the table. Request some one to select one end of the row and to take one, two, or three matches from it, you having the same privilege at the other end; and you guarantee he will be compelled to take the last match no matter how he may vary the number he takes.
The secret is to remove four matches each time between you. For instance, if your opponent takes three you take one; if he takes two you take two; if he takes one you take three and so on. It is obvious if four matches are taken six times one match will be left on the table, which your opponent must take.