medium   Probability

Game Off I

A release-checked medium problem for training Law of Total Probability, Conditional Probability.

Question

Suppose $0 < p < 1$. Alice and Bob play game. The game consists of $3$ points. For the first point of each game, Alice has probability $p$ of winning, while Bob has probability $1-p$ of winning. For the other two points of the game, the winner of the previous round has probability $p$ of winning, while the loser has probability $1-p$ of winning. A winner is declared when someone wins two consecutive points. If neither player wins two consecutive points, the entire game replayed under the same rules until a winner is declared. Find the probability that Bob wins when $p = 1/3$.

Practice focus

This Probability problem is tagged Law of Total Probability, Conditional Probability. State the random variables and conditioning information explicitly, then check the result against boundary cases before opening hints or a solution.

Explore related collections

Reviewed questions in this area

easyBaby BoyReviewed

Probability · SIG, DE Shaw

easyBad BagelReviewed

Probability · SIG, Jane Street