@surya_prakash There are 200 students in a class. 20% students are there who don’t like any subject. 50% students like physics, 60% students like Chemistry and 70% students like Mathematics. I + II + III = 100 - 20 = 80......(1) I + 2II + 3III = 50+60+70 = 180.....(2) Now if we put I = 0 then II + III = 80....(3) 2II + 3III = 180....(4) II should be maximum so that III cold be minimum. Now equation (4) - 2 x equation (3) III = 20. This 20 is percent actually. 20% of 200 = 40. I hope it's clear now.