primary number test. Frankly I don't think this is a right question to ask to check once analytical capabilities the questions like these are more of puzzles, if a person have anytime come across methods to solve (Heuristic tests, Fast deterministic tests) then only he will be able to answer it. I have taken lot of interview my self and attended some with my seniors as well, I will recommend to have Scenario based question instead of puzzles. Just a suggestion no offence.