If 20% of the students who failed in C++ failed in exactly 4 papers, then total how many students failed in C++?
Suppose total number of students who failed in C++ = x. 20% of the students failed in exactly 4 subjects, then % of students who failed in exactly 5 subject = 30%. Now 30% of x = 180. So x = 600. So 600 students failed in C++.