If that's important for his company, why not? It's like the people that apply for a programming job and complain they get O(n) questions. Also, it doesn't just

If that's important for his company, why not? It's like the people that apply for a programming job and complain they get O(n) questions. Also, it doesn't just test if they took it. It also tests whether they understood it and can apply it. (You would expect the schools to do that, but...) Of course, if this question requires combinatorial knowledge, and its irrelevant or not critical for the job, then that's just bad.