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Question

A, B, C are three mutually exclusive and exhaustive events associated with a random experiment. If \(3P(B) = 4P(A)\) and \(3P(C) = 2P(B)\), then what is \(P(A)\) equal to?

This question was previously asked in
NDA 2 2024 GAT Question Paper (01-Sep-2024)
The correct answer is
9/29

Understanding Probability Concepts for Events A, B, C

This problem involves understanding the properties of mutually exclusive and exhaustive events in probability.

  • Mutually Exclusive Events: These are events that cannot occur at the same time. If events A, B, and C are mutually exclusive, it means that the occurrence of one event precludes the occurrence of the others. Mathematically, \(P(A \cap B) = 0\), \(P(A \cap C) = 0\), and \(P(B \cap C) = 0\).
  • Exhaustive Events: These are events that cover all possible outcomes of an experiment. If events A, B, and C are exhaustive, their union represents the entire sample space, meaning \(P(A \cup B \cup C) = 1\).

For mutually exclusive and exhaustive events, the sum of their individual probabilities is equal to 1:

\( P(A) + P(B) + P(C) = 1 \)

Analyzing Given Probability Relationships

The question provides the following relationships between the probabilities of events A, B, and C:

  1. \(3P(B) = 4P(A)\)
  2. \(3P(C) = 2P(B)\)

From the first relationship, we can express \(P(B)\) in terms of \(P(A)\): \( P(B) = \frac{4}{3} P(A) \)

From the second relationship, we can express \(P(C)\) in terms of \(P(B)\): \( P(C) = \frac{2}{3} P(B) \)

Calculating P(A) Step-by-Step

Now, let's substitute the expression for \(P(B)\) into the equation for \(P(C)\) to get \(P(C)\) in terms of \(P(A)\): \( P(C) = \frac{2}{3} \left( \frac{4}{3} P(A) \right) \) \( P(C) = \frac{8}{9} P(A) \)

We know that for these mutually exclusive and exhaustive events, the sum of their probabilities is 1:

\( P(A) + P(B) + P(C) = 1 \)

Substitute the expressions for \(P(B)\) and \(P(C)\) in terms of \(P(A)\) into this equation:

\( P(A) + \frac{4}{3} P(A) + \frac{8}{9} P(A) = 1 \)

To solve for \(P(A)\), find a common denominator, which is 9:

\( \frac{9}{9} P(A) + \frac{12}{9} P(A) + \frac{8}{9} P(A) = 1 \)

Combine the terms on the left side:

\( \left( \frac{9 + 12 + 8}{9} \right) P(A) = 1 \) \( \frac{29}{9} P(A) = 1 \)

Finally, isolate \(P(A)\):

\( P(A) = \frac{9}{29} \)

Therefore, the probability of event A, \(P(A)\), is 9/29.

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