When an experiment is conducted, one and only one of three mutually exclusive events S₁, S₂, and S₃ can occur, with

P(S₁) = 0.4,

P(S₂) = 0.5,

and

P(S₃) = 0.1.

The probabilities that a fourth event A occurs, given that event S₁, S₂, or S₃ has occurred, are

P(A|S₁) = 0.4 P(A|S₂) = 0.2 P(A|S₃) = 0.1.