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If A and B are two independent events su...

If A and B are two independent events such that `P(A) gt (1)/(2), P(A nn B^(C ))=(3)/(25) and P(A^(C )nnB)=(8)/(25)`, then `P(A)` is equal to `("where, "A^("c") and B^("c")` represent the complement of events A and B respectively)

A

`(1)/(5)`

B

`(3)/(5)`

C

`(3)/(4)`

D

`(4)/(5)`

Text Solution

AI Generated Solution

The correct Answer is:
To solve the problem, we need to find the probability \( P(A) \) given the conditions about events A and B. ### Step-by-Step Solution: 1. **Define the Variables**: Let \( P(A) = x \) and \( P(B) = y \). We know that \( P(A) > \frac{1}{2} \). 2. **Use the Given Information**: - From the problem, we have: \[ P(A \cap B^C) = P(A) \cdot P(B^C) = x(1 - y) = \frac{3}{25} \] - This can be rewritten as: \[ x - xy = \frac{3}{25} \quad \text{(Equation 1)} \] 3. **Use the Other Given Information**: - The second piece of information gives us: \[ P(A^C \cap B) = P(A^C) \cdot P(B) = (1 - x)y = \frac{8}{25} \] - This can be rewritten as: \[ y - xy = \frac{8}{25} \quad \text{(Equation 2)} \] 4. **Set Up the Equations**: - From Equation 1: \[ x - xy = \frac{3}{25} \implies xy = x - \frac{3}{25} \quad \text{(Equation 3)} \] - From Equation 2: \[ y - xy = \frac{8}{25} \implies xy = y - \frac{8}{25} \quad \text{(Equation 4)} \] 5. **Equate the Two Expressions for \( xy \)**: - From Equation 3 and Equation 4, we can set them equal: \[ x - \frac{3}{25} = y - \frac{8}{25} \] - Rearranging gives: \[ x - y = -\frac{5}{25} \implies x - y = -\frac{1}{5} \implies y = x + \frac{1}{5} \quad \text{(Equation 5)} \] 6. **Substitute Equation 5 into Equation 1**: - Substitute \( y \) from Equation 5 into Equation 1: \[ x(1 - (x + \frac{1}{5})) = \frac{3}{25} \] - This simplifies to: \[ x(1 - x - \frac{1}{5}) = \frac{3}{25} \implies x(\frac{4}{5} - x) = \frac{3}{25} \] - Multiplying through by 25 to eliminate the fraction: \[ 25x(\frac{4}{5} - x) = 3 \implies 20x - 25x^2 = 3 \] - Rearranging gives: \[ 25x^2 - 20x + 3 = 0 \] 7. **Solve the Quadratic Equation**: - Using the quadratic formula \( x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \): \[ x = \frac{20 \pm \sqrt{(-20)^2 - 4 \cdot 25 \cdot 3}}{2 \cdot 25} \] \[ = \frac{20 \pm \sqrt{400 - 300}}{50} = \frac{20 \pm \sqrt{100}}{50} = \frac{20 \pm 10}{50} \] - This gives us two potential solutions: \[ x = \frac{30}{50} = \frac{3}{5} \quad \text{or} \quad x = \frac{10}{50} = \frac{1}{5} \] 8. **Select the Valid Solution**: - Since \( P(A) > \frac{1}{2} \), we discard \( \frac{1}{5} \) and keep: \[ P(A) = \frac{3}{5} \] ### Final Answer: \[ P(A) = \frac{3}{5} \]
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