Single correct option
Two fair six-sided dice are thrown. 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. 17/36
Show answer and solution
Answer: (B) 5/12
Possible prime sums: 2, 3, 5, 7, 11.
Number of outcomes: sum 2 → 1, sum 3 → 2, sum 5 → 4, sum 7 → 6, sum 11 → 2. Total = 15.
Probability = 15/36 = 5/12.
Don't forget 11 (5+6, 6+5) and don't count 9 (= 3 × 3) as prime.
Number of outcomes: sum 2 → 1, sum 3 → 2, sum 5 → 4, sum 7 → 6, sum 11 → 2. Total = 15.
Probability = 15/36 = 5/12.
Don't forget 11 (5+6, 6+5) and don't count 9 (= 3 × 3) as prime.
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