Prove that = 0. please give an answer with clear explanations.

If n[p(a)] = 64, then n(a)=?

In an exam 80% of the students passed in Eng, 85% in Math and 75% in both. If 40 students failed in both subjects. What is the total number of students?

In a survey of 200 students of a school, it was found that 120 students study Mathematics 90, study Physics, and 70 study Chemistry, 40 study Mathematics and Physics, 30 study Physics and Chemistry, 50 study Chemistry and Mathematics and 20 none of these subjects. Find the number of students who study all three subjects.

Let S = The set of all leap years between 1882 and 1906.

Find the Cardinal number of this set.