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Provide solution for RD Sharma maths class 12 chapter Probability exercise 30.7 question 18

Answers (1)

Answer:

 \frac{36}{61}

Hint:

 Use Baye’s theorem.

Given:

 Three win A, B, C contain 6 red and 4 white; 2 red, 6 white and 1 red 5 white ball respectively. A win is chosen at random and ball is drawn. If ball drawn is found to red. Find the probability that ball from win A.

Solution:

Let E1 and  E2  denotes the event that ball is red, bag A chose B chosen and bag C chosen respectively.

\begin{aligned} &P(E_1)=\frac{1}{3}\\ &P(E_2)=\frac{1}{3}\\ &P(E_3)=\frac{1}{3}\\ &P\left ( \frac{A}{E_1} \right )=\frac{6}{10}=\frac{3}{5}\\ &P\left ( \frac{A}{E_2} \right )=\frac{2}{8}=\frac{1}{4}\\ &P\left ( \frac{A}{E_3} \right )=\frac{1}{6}\\ \end{aligned}

Using Baye’s theorem we get

\begin{aligned} &P\left (\frac{E_1}{A} \right )=\frac{P(E_1).P\left ( \frac{A}{E_1} \right )}{P(E_1)\times P\left ( \frac{A}{E_1} \right )+P(E_2)\times P\left ( \frac{A}{E_2} \right )+P(E_3)\times P\left ( \frac{A}{E_3} \right )}\\ &=\frac{{\frac{1}{3}\times \frac{3}{5} }}{\frac{1}{3}\times \frac{3}{5}+\frac{1}{3}\times \frac{1}{4}+\frac{1}{3}\times \frac{1}{6}}\\ &=\frac{\frac{3}{5}}{\frac{3}{5}+\frac{1}{4}+\frac{1}{6}}\\ &=\frac{36}{61} \end{aligned}

Posted by

Gurleen Kaur

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