A deadly game of chance

Aaron, Benjamin, Charlie, and Daniel are stuck on an island. They are then saved by a pirate, but as we all know, pirates won’t just save the lives of people for free. Therefore, the pirate invents a game of death for them to play. The four of them will take turns in alphabetical order drawing cards from a deck of cards (without Jokers). They will then put their card back in the pile and shuffle the cards. The first one to draw the ace of spades will walk the plank, and the rest of them will survive.

What is the probability that Daniel will survive? Round to the nearest thousandth.


The answer is 0.757.

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1 solution

Steven Yuan
Mar 8, 2018

The easiest way to solve this problem is through complements: find the probability that Daniel does not survive, then subtract that value from 1 to find the probability that he will survive.

Suppose the game ends after only one round. That means Aaron, Benjamin, and Charlie all chose cards that were not the ace of spades, then Daniel chose the ace of spades. This happens with probability ( 51 52 ) 3 ( 1 52 ) . \left ( \dfrac{51}{52} \right )^3 \left ( \dfrac{1}{52} \right ). If the game ends after two rounds, then all four people chose non-ace of spades cards during the first round, then in the second round Daniel is the first to draw the ace of spades. This happens with probability ( 51 52 ) 7 ( 1 52 ) . \left ( \dfrac{51}{52} \right )^7 \left ( \dfrac{1}{52} \right ). In general, if the game lasts n n rounds, the probability that Daniel loses is ( 51 52 ) 4 n 1 ( 1 52 ) , \left ( \dfrac{51}{52} \right )^{4n - 1} \left ( \dfrac{1}{52} \right ), and the overall probability that he loses is

n = 1 ( 51 52 ) 4 n 1 ( 1 52 ) = ( 51 52 ) 3 ( 1 52 ) 1 ( 51 52 ) 4 = 5 1 3 5 2 4 5 1 4 . \begin{aligned} \sum_{n = 1}^{\infty} \left ( \dfrac{51}{52} \right )^{4n - 1} \left ( \dfrac{1}{52} \right ) &= \dfrac{ ( \frac{51}{52} )^3 ( \frac{1}{52} )}{1 - ( \frac{51}{52} )^4} \\ &= \dfrac{51^3}{52^4 - 51^4}. \end{aligned}

Therefore, the probability that Daniel will survive is 1 5 1 3 5 2 4 5 1 4 0.757 . 1 - \dfrac{51^3}{52^4 - 51^4} \approx \boxed{0.757}.

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