If 75% students in a class answered the first questions on a certain test correctly. 55% answered the second question on the test correctly and 20% answered neither of the questions correctly. What percentage of students answered both the questions correctly?

here, if number of student is 100 1st question answered correctly = n(F)= 75 2nd     "           "               "        = n(S)= 55 neither "           "              "          = n(FUS)' = 100-20=80 Both question answered correctly = n(F∩S)=? n(FUS)= 100- n(FUS)'=100-20 =80 here, n(FUS)= n(F) +n(S)-n(F∩S) or,n(F∩S)=75+55-80 =50