CA Foundation · Quantitative Aptitude · Permutations and Combinations
If nC2 = 66, what is the value of n+1C3?
The answer is 286. From n(n-1)/2 = 66, n = 12. Therefore (n+1)C3 = 13C3 = (13×12×11)/6 = 286. Using 12C3 = 220 would ignore the added one in the upper number.
- A286Correct
- B220
- C364
- D165
Explanation
nC2 = n(n-1)/2 = 66 gives n(n-1) = 132, so n = 12. Then n+1C3 = 13C3 = (13×12×11)/6 = 286. Choosing 12C3 = 220 is the mistake of ignoring the +1.
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