4 Rowan and Colin are playing a game of 'scissors-paper-rock'. In each round of this game, each player chooses one of scissors ( $\$$ ), paper ( $\square$ ) or rock ( $\bullet$ ). The players reveal their choices simultaneously, using coded hand signals. Rowan and Colin will play a large number of rounds. At the end of the game the player with the greater total score is the winner.

The rules of the game are that scissors wins over paper, paper wins over rock and rock wins over scissors. In this version of the game, if a player chooses scissors they will score $+ 1,0$ or - 1 points, according to whether they win, draw or lose, but if they choose paper or rock they will score $+ 2,0$ or - 2 points. This gives the following pay-off tables.\\
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(i) Use an example to show that this is not a zero-sum game.\\
(ii) Write down the minimum number of points that Rowan can win using each strategy. Hence find the strategy that maximises the minimum number of points that Rowan can win.

Rowan decides to use random numbers to choose between the three strategies, choosing scissors with probability $p$, paper with probability $q$ and rock with probability $( 1 - p - q )$.\\
(iii) Find and simplify, in terms of $p$ and $q$, expressions for the expected number of points won by Rowan for each of Colin's possible choices.

Rowan wants his expected winnings to be the same for all three of Colin's possible choices.\\
(iv) Calculate the probability with which Rowan should play each strategy.

\hfill \mbox{\textit{OCR D2 2016 Q4 [10]}}