Interview Q&A / Aptitude

1. What is the difference between permutations and combinations, and how do you know which to use?

   Use permutations when order matters, like choosing a captain and vice-captain, and combinations when order does not matter, like choosing a committee. nPr = n! / (n - r)! and nCr = n! / (r! x (n - r)!). Each combination of r items can be arranged in r! ways, so nPr = nCr x r!.

   AdvancedIn-depth4 min read
2. In how many ways can a committee of 5 be formed from 6 men and 4 women so that it has at least 2 women?

   186. Total committees C(10,5) = 252. Subtract those with no woman, C(6,5) = 6, and with exactly one woman, 4 x C(6,4) = 60. 252 - 66 = 186.

   AdvancedQuick answer1 min read