Single correct option
Two fair six-sided dice are thrown together. What is the probability that the sum of the numbers shown is a prime number?
- A. 1/2
- B. 1/3
- C. 5/12
- D. 7/18
Show answer and solution
Answer: (C) 5/12
Possible prime sums: 2, 3, 5, 7, 11.
Number of ways: sum 2 → 1, sum 3 → 2, sum 5 → 4, sum 7 → 6, sum 11 → 2. Total = 15.
Probability = 15/36 = 5/12.
Tip: The number of ways to get sum s with two dice is (s − 1) for s ≤ 7 and (13 − s) for s ≥ 7.
Number of ways: sum 2 → 1, sum 3 → 2, sum 5 → 4, sum 7 → 6, sum 11 → 2. Total = 15.
Probability = 15/36 = 5/12.
Tip: The number of ways to get sum s with two dice is (s − 1) for s ≤ 7 and (13 − s) for s ≥ 7.
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