CA Foundation · Quantitative Aptitude · Permutations and Combinations
If nC8 = nC12, what is the value of nC5?
Since nC8 = nC12, n equals 8 + 12 = 20. Therefore nC5 = 20C5 = 15504. This uses the property that nCr = nCs means either r = s or r + s = n.
- A15504Correct
- B11628
- C20
- D4368
Explanation
nCr = nCs implies r + s = n, so n = 8 + 12 = 20. Then 20C5 = (20×19×18×17×16)/120 = 1860480/120 = 15504. The value 11628 is 19C5... actually it is 19C5? 19C5 = 11628, so it comes from using n = 19 by mistake.
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