ProbabilityHard

Question

For any two events A and B in a sample space

Options

A.PP(B) ≠ 0 is always true
B.P(A ∩ ) = P(A) - P(A ∩ B) does not hold
C.P(A ∪ B) = 1- P()P() if A and B are independent
D.P(A ∪ B) = 1- P()P() if A and B are disjoint

Solution

We know that,
      P
Since, P(A ∪ B) < 1
⇒     - P(A ∪ B) > - 1
⇒     P(A) + P(B) - P(A ∪ B) > P(A) + P(B) -1
⇒    
⇒     P
Option (a) is correct.
The choice (b) holds only for disjoint ie, P(A ∩ B) = 0
Finally, P(A ∪ B) = P(A) + P(B) - P(A ∩ B)
      = P(A) + P(B) - P(A).P(B)
If A,B are independent
      = 1 - {1 - P(A)} {1 - P(B)}
      = 1 - P().P()
∴     Option (c) is correct, but option (d) is not correct.

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