If C(n, 2) = 45, find the value of n.

A8

B9

C10

D12

Explanation

C(n, 2) = n(n-1) / 2 = 45 => n(n-1) = 90 => n^2 – n – 90 = 0 => (n – 10)(n + 9) = 0 => n = 10.

Exam Relevance

Topic: Permutations & Combinations
Subtopic: Combinations

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