Asked by: Nicholas Young, Cambridge
The ancient Chinese game of rock-paper-scissors is governed by three simple rules: rock beats scissors, scissors beats paper, paper beats rock. On the face of it, the chances of winning are just one in three, but that presumes people pick rock, paper or scissors at random.
In fact, studies have shown that our choice often depends on what happened in the previous game. Losers tend to switch to the choice that would have won the game they just lost, while winners tend to stick. And these habits can be exploited as follows: if you won, then play what your opponent just used, but if you lost, then play what neither of you played. That can tilt the odds in your favour.
Robert is a science writer and visiting professor of science at Aston University.