If in a class of 100 students, 60 like mathematics, 72 like physics, 68 like chemistry and no student likes all three subjects, then the number of students who didn't like mathematics and chemistry is ?
n(M∪P∪C)=n(M)+n(P)+n(C)−n(M∩P)−n(M∩C)−n(P∩C)
100=60+72+68−(x+y+z)+0⇒x+y+z=100
So no student like only maths, or only physics or only chemistry
x+y=60x+z=72y+z=68⎫⎪⎬⎪⎭⇒y=28
Now,
n(M′∩C′)=100−n(M∪C)=100−(60+68−y)=28−28=0