Difficulty: Easy
Correct Answer: 5005
Explanation:
Introduction / Context:We are forming groups (unordered selections). This is a direct application of combinations: the number of ways to pick k people from n distinct people is C(n, k).
Given Data / Assumptions:
Concept / Approach:Use C(n, k) = n! / (k! (n − k)!). Here n = 15 and k = 6.
Step-by-Step Solution:
C(15, 6) = 15! / (6! * 9!)Compute via product form: (151413121110) / (654321) = 5005.Verification / Alternative check:Symmetry C(15, 6) = C(15, 9) holds; calculators or Pascal-style reasoning confirm 5005.
Why Other Options Are Wrong:5000 and 5050 are close but not exact; “None of these” is not needed because 5005 is precise.
Common Pitfalls:Accidentally treating it as permutations (ordering groups), which would overcount.
Final Answer:5005
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