Concept: The question tests on the area of Modern Math (Counting/Combinatorics)
Solution:
The total number of ways of choosing at least 1 from n distinct objects is 2^n - 1
here n = 5
Therefore the total number of ways = 2^5 - 1 = 31
Another way of looking at this is that if we have to find the number of ways he can fail, then he can fail in 1 subject or 2 subjects or 3 subjects or 4 or 5 subjects
= 5C1 + 5C2 + 5C3 + 5C4 + 5C5
= 5 + 10 + 10 + 5 + 1
= 31
(option d)