Each of 74 students in a class studies at least one of the three subjects H, E and P. Ten students study all three subjects, while twenty study H and E, but not P. Every student who studies P also studies H or E or both. If the number of students studying H equals that studying E, then the number of students studying H is
Let the number of students studying only H be h, only E be e, only H and P but not E be x, only E and P but not H be y.
Only P = 0
All three = 10
Studying only H and E but not P = 20
Number of students studying H = Number of students studying E
h + x + 20 + 10 = e + y + 20 + 10
h + x = e + y
Total number of students = 74
h + x + 20 + 10 + e + y = 74
h + x + e + y = 44
h + x + h + x = 44
h + x = 22
Therefore, the number of students studying H = h + x + 20 + 10
= 22 + 20 + 10 = 52
The correct answer is 52.