The Fifteen Game Puzzles
Puzzles
Rules — The Fifteen game
- The numbers 1 to 9 sit on the board. In turn, each player takes one into their own box: that number leaves the board and nobody else can take it.
- Whoever collects in their box three numbers that add up to 15 wins. You may hold more than three numbers — it is enough for any three of them to add up to 15.
Levels:
- Level 1 — Fifteen. The classic: whoever first makes 15 wins.
- Level 2 — Fifteen in reverse. Same rules, but collecting three numbers that add up to 15 makes you LOSE.
- Level 3 — Double sum. Played with nine tiles carrying two numbers each (1 to 3) instead of one. Whoever collects three tiles whose first digits add up to a multiple of 3, and whose second digits also add up to a multiple of 3, wins.
Note: on this level whoever starts wins with perfect play, so it is good practice against the computer but not for competitions.
Watch a game between Ann and Bob. Every number taken leaves the board and goes into the box of whoever took it.
Look: Ann has FOUR numbers in her box (1, 4, 5 and 6) and she still won. They do not all need to add up to 15: it is enough for THREE of them to add up to 15. The 1 is left over and does not matter.
In each puzzle, the player to move can win. Find out how: the computer will defend as well as it can.