Single correct option
Two fair six-sided dice are rolled together. What is the probability that the sum of the numbers shown is a prime number?
- A. 1/3
- B. 5/12
- C. 7/18
- D. 1/2
Show answer and solution
Answer: (B) 5/12
Possible prime sums: 2, 3, 5, 7, 11.
Ways: sum 2 → 1; sum 3 → 2; sum 5 → 4; sum 7 → 6; sum 11 → 2. Total = 15 of 36 equally likely outcomes.
Probability = 15/36 = 5/12.
Common errors: forgetting sum 11 (13/36) or treating 9 as prime.
Ways: sum 2 → 1; sum 3 → 2; sum 5 → 4; sum 7 → 6; sum 11 → 2. Total = 15 of 36 equally likely outcomes.
Probability = 15/36 = 5/12.
Common errors: forgetting sum 11 (13/36) or treating 9 as prime.
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