UPSC NDA Math Model Paper 9

Here, P(A) = 1/2, P(B) = 1/3, P(C) = 1/4.
Probability of at least one of the three events occurs = 1 - None of the event occuring
= 1 - (1 - 1/2) × (1 - 1/3) × (1 - 1/4)
= 1 - (1/2) × (2/3) × (3/4)
= 1 - 1/4
= 3/4
Hence, option (3) is correct.