Two standard dice are thrown simultaneously. What is the probability that the sum of the two upper faces equals 8?
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A2/9
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B5/36
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C1/6
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DData Inadequate
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E7/36
Answer
Correct Answer: 5/36
Explanation
Introduction / Context:Rolling two fair six-sided dice yields 36 equally likely ordered pairs. We want the chance that the sum is exactly 8.
Given Data / Assumptions:
- Die outcomes are 1–6.
- Sample space size = 6 × 6 = 36.
- Sum target = 8.
Concept / Approach:Enumerate the pairs whose coordinates sum to 8 and divide by 36.
Step-by-Step Solution:Favorable pairs: (2,6), (3,5), (4,4), (5,3), (6,2) → 5 outcomes.Probability = 5 / 36.
Verification / Alternative check:Check neighboring sums: sums of 7 have 6 outcomes (symmetric peak), sums of 8 have 5, consistent with standard sum distribution.
Why Other Options Are Wrong:2/9 ≈ 8/36 (too large); 1/6 = 6/36 (wrong count); “Data Inadequate” is inappropriate since the model is standard.
Common Pitfalls:Forgetting that ordered pairs (3,5) and (5,3) are distinct outcomes.
Final Answer:5/36