A college survey was taken to determine where student study. Of157 student surveyed, 93 studied in the library, 87 studied in the student union, 33 studies in both the library and the student union. Of those interviewed how many studied only in the library?

Question

anonymous · Answer

I think there's an error in the question. 
But anyway, since 93 studied in the library in total, and out of those 93, 33 of them also studied in the student union, 60 of them ONLY studied in the library.