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