[ggggtez]

I'd like to highlight this comment for everyone who is saying the question can only be gotten wrong by someone who misreads it.

It can be easy for people to forget that many people (even coders) have never done this type of math before.

[cdf2theworld]

I believe CS degrees require discreet math (and highschool algebra 2), which means they've done permutations and combinatorics, so yes they've done these types of problems before. The real question is how long has it been?