The dormitory students of Marian were asked whether they had a dictionary or thesaurus in their rooms. The result showed that 650 students has a dictionary. 150did not have a dictionary, 175 had a thesaurus and 50 had neither a dictionary nor a thesaurus. Find the number of students who (a) Live in the dormitory (b) Have both a dictionary and a thesaurus (c) Have only a thesaurus.​