You probably are rejecting potentially good candidates, but I would personally suggest that of the developers that I want to hire, most of them are members of t

You probably are rejecting potentially good candidates, but I would personally suggest that of the developers that I want to hire, most of them are members of the set of developers who know what the modulo operator is for. And since hiring is a numbers game, it seems like a reasonable filter. Besides, you are allowed to ask other questions in the interview.