Find P(A'/B'), given P(A) = 3/4, P(B) = 9/20 and P(AB) = 1/4?

This question was previously asked in
SSC CGL Tier-II ( JSO ) 2017 Official Paper ( Held On : 22 Feb 2018 )
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  1. 1/20
  2. 1/9
  3. 1/11
  4. 1/12

Answer (Detailed Solution Below)

Option 3 : 1/11
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Detailed Solution

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Given:

P(A) = 3/4

P(B) = 9/20

P(A ∩ B) = 1/4

Calculation:

P(A ∪ B) = P(A) + P(B) – P(A ∩ B)

= 3/4 + 9/20 – 1/4

= 19/20

P(A'/B') = P(A' ∩ B')/P(B')= 1 – P(A ∪ B)'/[1 – P(B)]

= [1 – 19/20]/[1 – 9/20]

=1/11

∴  Probability P(A'/B') is 1/11.

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