Q1. 4 Events: Event C. Event E1. Event E2. Event E3
P(C) = 0.15 P(E1)=P(E3)=P(E2)=0.3
p(K/E1)=0.08 P(K/E2)=0.04 P(K/E3)=0.01 P(k/C)=0.15
Ask: What is probability that given not K (K'=1-P(k)), and it would be one of the event in E3? P(E3/K')?
P(C) = 0.15,
P(E1)=P(E2)=P(E3)=0.3
P(K|E1)=0.08, P(K|E2)=0.04,
P(K|E3)=0.01, P(K|C)=0.15
P(E3|Kc) = ?
First using total law of probability, we find P(K)
P(K) = P(E1)P(K|E1) +
P(E2)P(K|E2) +
P(E3)P(K|E3)+P(C)P(K|C)
P(K) = (0.3 x 0.08) + (0.3 x 0.04) + (0.3 x 0.01) + (0.15 x
0.15)
P(K) = 0.0615
By definition of conditional probability:
P(E3|Kc) = P(E3 ∩ Kc) /
P(Kc)
P(Kc) = 1 - P(K) = 1 - 0.0615 = 0.9385
P(E3∩Kc) =
P(E3)P(Kc|E3) = P(E3)
(1 - P(K|E3)) = 0.3 x (1 - 0.01) = 0.297
P(E3|Kc) = 0.297 / 0.9385 =
0.3165
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