Colour of the final cherry eaten from two bowls
Question
Bowl A has red and green cherries; bowl B has red and green. Repeat the following until every cherry is gone: if bowl B is not empty, move a randomly chosen cherry from B to A; then eat a randomly chosen cherry from A. What is the probability, rounded to five decimal places, that the very last cherry eaten is red?
Short answer
About . Track one cherry at a time. During the transfer rounds bowl A always holds cherries when one is eaten, and the final are eaten in random order. An original A cherry is last with probability ; a B cherry moved in round (uniform on –) with probability . Weighting by colour gives .
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Open the worked solutionLessons behind this question
- Sample Spaces, Events, and the Probability Axioms
- Conditional Probability, Total Probability, and Bayes' Rule
- Worked Examples — Probability Trees, Monty Hall, and Bayesian Updating
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