Three dice rolled: at least one shows 2: Three fair six-faced dice are rolled. How many outcomes in the 6^3 sample space have at least one die showing 2?
Aptitude
Permutation and Combination
Difficulty: Easy
Choose an option
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A36
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B81
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C91
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D116
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ENone of these
Answer
Correct Answer: 91
Explanation
Introduction / Context:Counting “at least one” events on dice is best done via the complement rule: subtract the count with no 2s from the total sample space of 6^3 equiprobable outcomes.
Given Data / Assumptions:
- Three independent fair dice, faces {1,…,6}.
- We count ordered triples (d1, d2, d3).
Concept / Approach:
- Total outcomes = 6^3.
- No-2 outcomes: each die has 5 allowed faces (exclude 2) → 5^3.
- At least one 2 = 6^3 − 5^3.
Step-by-Step Solution:
Total = 6^3 = 216No-2 = 5^3 = 125Count = 216 − 125 = 91Verification / Alternative check:Inclusion–exclusion by exact number of 2s (1, 2, 3) yields the same 91; complement is simpler.
Why Other Options Are Wrong:
- 36 and 81 are too small; 116 exceeds total remaining after subtraction.
Common Pitfalls:
- Mixing “count of outcomes” with “probability.”
Final Answer:91