Question #1: He eliminated 1 of the 3 choices. So the probability of getting correct answer is 1/2.
Question #2: He eliminated 1 of the 3 choices. So the probability of getting correct answer is 1/2.
For Question #3-5: The probability of getting correct answer is 1/3 and getting incorrect it 2/3.
He should get at least 2 out of 3 correctly answered. The probability would be :-
P(at least 2 correct out of 3) = P(exactly 2 correct) + P(all 3 correct)

Combined probability would be =
