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If A and B are independent events, then which of the following is/are true?

(A) Aˉ\bar{A} and B are independent events

(B) P(A∩B)=0P(A \cap B) = 0

(C) Aˉ\bar{A} and Bˉ\bar{B} are independent events

(D) P(A∩B)=P(A)+P(B)P(A \cap B) = P(A) + P(B)

Choose the correct answer from the options given below:

Solution

✅ Correct Option: 1

When A and B are independent events:

P(A∩B)=P(A)×P(B)P(A \cap B) = P(A) \times P(B)

This means one event happening does not affect the probability of the other.


Statement (A): Aˉ\bar{A} and B are independent

P(Aˉ∩B)=P(B)−P(A∩B)P(\bar{A} \cap B) = P(B) - P(A \cap B)

=P(B)−P(A)×P(B)= P(B) - P(A) \times P(B)

=P(B)×[1−P(A)]= P(B) \times [1 - P(A)]

=P(B)×P(Aˉ)= P(B) \times P(\bar{A})

Therefore, Aˉ\bar{A} and B are independent.


Statement (B): P(A∩B)=0P(A \cap B) = 0

For independent events: P(A∩B)=P(A)×P(B)P(A \cap B) = P(A) \times P(B)

This equals 0 only if P(A)=0P(A) = 0 or P(B)=0P(B) = 0.

Example: Tossing a coin twice where A = first toss is heads and B = second toss is heads.

P(A)=0.5P(A) = 0.5, P(B)=0.5P(B) = 0.5

P(A∩B)=0.5×0.5=0.25≠0P(A \cap B) = 0.5 \times 0.5 = 0.25 \neq 0

Independent events can happen together, so this statement is false.


Statement (C): Aˉ\bar{A} and Bˉ\bar{B} are independent

P(Aˉ∩Bˉ)=1−P(A∪B)P(\bar{A} \cap \bar{B}) = 1 - P(A \cup B)

=1−[P(A)+P(B)−P(A∩B)]= 1 - [P(A) + P(B) - P(A \cap B)]

=1−P(A)−P(B)+P(A)×P(B)= 1 - P(A) - P(B) + P(A) \times P(B)

=[1−P(A)]×[1−P(B)]= [1 - P(A)] \times [1 - P(B)]

=P(Aˉ)×P(Bˉ)= P(\bar{A}) \times P(\bar{B})

Therefore, Aˉ\bar{A} and Bˉ\bar{B} are independent.


Statement (D): P(A∩B)=P(A)+P(B)P(A \cap B) = P(A) + P(B)

For independent events: P(A∩B)=P(A)×P(B)P(A \cap B) = P(A) \times P(B)

The formula P(A∩B)=P(A)+P(B)P(A \cap B) = P(A) + P(B) is mathematically incorrect.

Note: P(A∪B)=P(A)+P(B)−P(A∩B)P(A \cup B) = P(A) + P(B) - P(A \cap B) is the formula for union, not intersection.

This statement is false.


Statements (A) and (C) are true.

If A and B are independent, then all combinations remain independent: A and B, Aˉ\bar{A} and B, A and Bˉ\bar{B}, and Aˉ\bar{A} and Bˉ\bar{B}.

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