CA Foundation · Quantitative Aptitude · Permutations and Combinations

If nC2 = 45, how many ways can a team of 3 be selected from those n people?

The answer is 120. From nC2 = 45 we get n(n-1) = 90, so n = 10. A team of 3 from 10 people can be chosen in 10C3 = 120 ways.

Explanation

nC2 = n(n-1)/2 = 45 gives n(n-1) = 90, so n = 10. Then 10C3 = 120. Option 210 is 10C4, and option 90 is n(n-1), a common slip.

One question tells you little. A timed set on Permutations and Combinations shows your real accuracy, how long you take and where you lose marks.