Number of student who drinks at least one of them =12+5 + 8 + 10 + 20 +15 +10 =80
Hence,Number of student who did not drink any of this = 100 - 80 =20
Hence,Option (C) 20 is the correct chocie.
These types of problem falls in Set Theory.
and there is difference between x drinks coffee and x drinks " only " coffee.Please read question carefullly.