CMA Foundation · Fundamentals of Business Mathematics and Statistics · Permutation and Combinations
If nC2 = 45, what is the value of n?
The value of n is 10. Because nC2 equals n(n-1)/2, setting it equal to 45 gives n(n-1) = 90, which is satisfied by n = 10. Checking, 10C2 = 45, whereas 9C2 = 36 and 11C2 = 55.
- A9
- B10Correct
- C11
- D12
Explanation
nC2 = n(n-1)/2 = 45, so n(n-1) = 90 = 10×9, giving n = 10. Check: 10C2 = 45. Option 9 gives 36, and 11 gives 55.
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