Problem
COM-B1-M12-P019 Set 5. Two Piles
#19
★★★☆☆ Level 3 of 5
There are two piles of \(15\) and \(21\) stones. In one move, a player may take any positive number from one pile. The last move wins. Find a winning first move.
Make the piles equal.
The first player takes \(6\) stones from the pile \(21\), leaving two piles of \(15\). Then the first player copies the opponent’s move in the other pile. This strategy gives the first player the last move.
Pairing strategy.