Prime-faced dice with a prime total
Question
Two fair dice each have the six smallest primes, , on their faces. Both are rolled. What is the probability that the sum of the two faces is itself a prime number?
Short answer
. Two odd primes sum to an even number above 2, and , so a prime total needs exactly one die showing 2 and the other showing an odd prime with prime. That works for , each in two orders, giving of the outcomes.
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Open the worked solutionLessons behind this question
- Counting and Combinatorics
- Expectation, Mean, and Variance
- Conditional Probability, Total Probability, and Bayes' Rule
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