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AMO 2021 – Junior College (Grades 11–12) Question 24

AMO · AMO 2021 – Junior College (Grades 11–12)

Question 24

A frog starts at $(3,3)$ and stops as soon as it reaches either coordinate axis. From $(a,b)$ it moves independently to $(a-1,b)$, $(a,b-1)$ or $(a-1,b-1)$, each with probability $1/3$. If $p$ is the probability of stopping at $(0,0)$, find $81p$.

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