There must have been some type of an mistake/error in this question. If there are 50 that do not play sports, 70 that don't play music, and 40 that don't do either, that would add up (50 + 70 +40) to (=)160 students which would be more than the 100 students in school. If the question is truly written like that, I will do more research. For now, skip that question.