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If \(P(A\cap B) = 1/2\) and \(P(\overline{A}\cap\overline{B}) = 1/2\), and \(2P(A) = P(B) = k\), then what is the value of \(k\)?

This question was previously asked in
NDA 2 2026 GAT Question Paper (13-Sep-2026)
The correct answer is

2/3

Since \(\overline{A}\cap\overline{B}=\overline{A\cup B}\), we get \(P(A\cup B)=1-P(\overline{A}\cap\overline{B})=1-\frac12=\frac12\). Using \(P(A\cup B)=P(A)+P(B)-P(A\cap B)\) with \(P(A)=\frac{k}{2}\) and \(P(B)=k\) gives \(\frac{k}{2}+k-\frac12=\frac12\), so \(\frac{3k}{2}=1\) and \(k=\frac{2}{3}\).

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Similar Questions

  1. Two men hit at a target with probabilities 1/2 and 1/3 respectively. What is the probability that exactly one of them hits the target?

  2. Two similar boxes B i(i = 1, 2) contain (i + 1) red and (5 – i – 1) black balls. One box is chosen at random and two balls are drawn randomly. What is the probability that both the balls are of different colours?

  3. Consider the following relations for two events E and F:

    1. P(E ∩ F) ≥ P(E) + P(F) - 1

    2. P(E ∪ F) = P(E) + P(F) + P(E ∩ F)

    3. P(E ∪ F) ≤ P(E) + P(F)

    Which of the above relations is/are correct?

  4. What is \(\dfrac{P(A)+2P(B)}{3P(C)+P(D)}\) equal to?

  5. Consider the following statements for three events A, B and C:

    I. \(P(A\cap B\cap C) \le P(A)+P(B)+P(C)-2\)

    II. \(P(A\cup B\cup C) \ge P(A)+P(B)+P(C)\)

    Which of the statements given above is/are correct?


Important Questions from Addition Theorem of Events

  1. Two men hit at a target with probabilities 1/2 and 1/3 respectively. What is the probability that exactly one of them hits the target?

  2. Two similar boxes B i(i = 1, 2) contain (i + 1) red and (5 – i – 1) black balls. One box is chosen at random and two balls are drawn randomly. What is the probability that both the balls are of different colours?

  3. Consider the following relations for two events E and F:

    1. P(E ∩ F) ≥ P(E) + P(F) - 1

    2. P(E ∪ F) = P(E) + P(F) + P(E ∩ F)

    3. P(E ∪ F) ≤ P(E) + P(F)

    Which of the above relations is/are correct?

  4. What is \(\dfrac{P(A)+2P(B)}{3P(C)+P(D)}\) equal to?

  5. Consider the following statements for three events A, B and C:

    I. \(P(A\cap B\cap C) \le P(A)+P(B)+P(C)-2\)

    II. \(P(A\cup B\cup C) \ge P(A)+P(B)+P(C)\)

    Which of the statements given above is/are correct?

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