In her weekly guest blog post, Joanne talks about the probabilities involved in this popular game.
By Joanne Arcand
The other night, I was out for dinner with family and our waiter confessed to starring in a “mockumentary" about the world championships of the Rock Paper Scissors (RPS) society. The film, entitled “Rock, Paper, Scissors-The Way of the Tosser”, follows a competitor in the world rock,paper,scissors championship.
I know you’re just itching to compete.
I haven’t actually viewed the movie, but have seen a few trailers on youtube(I’m not sure the producer intended the unfortunate connotations of the word ‘tosser’, but as a ‘heads up’…usually not a playground friendly term). It has prompted a bit of internet diversion for me - perhaps here’s a sport I can get my left-handed-post-baby-belly-uncoordinated self behind. Plus, it appeals to my math side.
If you haven’t played “rock, paper, scissors” before, here’s the summary. Two players face each other and use one hand to compete(usually the right one). Holding that hand in a fist shape at first, move the fist up and down in front of the chest, counting on the down motion; “1…2….3…” during the forth down motion(called the ‘throw’ or ‘toss’), change the fist into one of the three shapes: closed fist is “rock”, flat horizontal hand is “paper”, and first two fingers outstretched horizontally is “scissors”. Rock beats scissors, Scissors beats paper, paper beats rock. Best two out of three wins.
First, the math side
Being somewhat of a math geek, I have used this as a probability lesson before. That is, I have tried to.
One would think that with three signs available, each sign would have a 33% chance of appearing in any given toss. Turns out not to be the case. It seems that scissors is the least thrown in any given tournament (likelihood of scissors: 29.6%). It might be the coordination of the scissor shape making it less likely to be chosen quickly. Or maybe there’s some psychological block against ‘running with scissors’ that prevents the use of simulated sharp pointy objects in class. Regardless, every time I have tried to do this in a math class, I get a strangely shaped graph with an itty,bitty ‘scissors’ bar.
So to win, drop the math and think psychology. My mom brain is now using it for all sorts of decision making-who gets to pick the TV show, whether tonight is a bath night, or how many vegetable pieces the picky eater has to struggle through. If you want to follow suit, here are the top five ‘hints’ for winning the “best three out of five.”
Top five rules for winning Paper, Rock, Scissors
- If playing with ‘newbies’, use paper more often. Since scissors is less likely to be thrown, your competitor is likely to throw ‘rock’ (which you would win) or ‘paper’ (which you would tie). According to the mantra “rock is for rookies” from the World RPS society, new players tend to play rock more often
- Try suggesting a throw. If you say something like “scissors beat paper, rock beats scissors (show rock), paper beats rock (show rock)” Believe it or not(I’ve only tried it on five year olds), the subconscious actually takes suggestions this way. After giving this suggestion, the opponent plays rock.
- If your opponent plays the same throw twice, they probably won’t play it a third time. Subconsciously, we want the game to be random and will purposefully avoid throwing the same throw three times. If you see paper twice, you can assume paper won’t be thrown the third time-play rock.
- When you’re stuck, try playing the throw that would have lost to the opponents previous throw. There’s strange psychology here, but it seems we like to telegraph our future moves by throwing the shape that would lose to the next throw. So your opponent plays scissors, the next throw would be rock…if you play paper, you win!
- “Cloak” scissors. Cloaking in the RPS world is the term for waiting until the last possible moment to show the sign. This can trick your opponent into thinking you’re throwing ‘rock’. They would then throw paper (to beat the rock) and your sneaky scissor sign would take the tournament.
Want to read more? Try the world RPS society! Happy tossing!
Joanne Arcand is trying to juggle her role as a math teacher with her other life as mom of twin boys. She lives in Oakville, Ontario.
