out of 320 students at a university,190 taking math,235 taking chemistry and 120 taking physics.125 are taking both chemistry and math,95 taking both chemistry AND PHYSIC,55 TAKING BOTH MATH AND PHYSICS.HOW MANY ARE TAKING ALL THE THREE SUBJECTS

Answer 1

http://math.stackexchange.com/questions/122384/venn-diagram-3-set

AUBUC=A+B+C-AVB-AVC-BVC+AVBVC

U is union, V is interstection
320=190+235+120-125-120-55+AVBVC

so solve for the intersection of all three courses, AVBVC
See the link.