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Need Solution for R.D.Sharma Maths Class 12 Chapter 30 Probability  Exercise 30.5 Question 23 Maths Textbook Solution.

Answers (1)

Answer:\frac{17}{42}

Hint: You must know the rules of finding probability functions.

Given:  Urn A = (4R+3B) = 7 balls

Urn B = (5R+4B) = 9 balls

Urn C = (4R+4B) = 8 balls

Solution

Urn A contain 4 red \left ( R_{1} \right ), 3 black \left ( B_{1} \right ) balls

Urn B contain 5 red \left ( R_{2} \right ), 4 black \left ( B_{2} \right ) balls

Urn B contain 4 red \left ( R_{3} \right ), 4 black \left ( B_{3} \right ) balls

P(3 balls drawn contain 2 red and a black ball)

\begin{aligned} &=P\left[\left(R_{1} \cap R_{2} \cap B_{3}\right) \cup\left(R_{1} \cap B_{2} \cap R_{3}\right) \cup\left(B_{1} \cap R_{2} \cap R_{3}\right)\right] \\\\ &=P\left(R_{1} \cap R_{2} \cap B_{3}\right)+P\left(R_{1} \cap B_{2} \cap R_{3}\right)+P\left(B_{1} \cap R_{2} \cap R_{3}\right) \\\\ &=P\left(R_{1}\right) \times P\left(R_{2}\right) \times P\left(B_{3}\right)+P\left(R_{1}\right) \times P\left(B_{2}\right) \times P\left(R_{3}\right)+P\left(B_{1}\right) \times P\left(R_{2}\right) \times P\left(R_{3}\right) \\\\ &=\frac{4}{7} \times \frac{5}{9} \times \frac{4}{8}+\frac{4}{7} \times \frac{4}{9} \times \frac{4}{8}+\frac{3}{7} \times \frac{5}{9} \times \frac{4}{8} \\\\ &=\frac{80+64+60}{504} \\\\ &=\frac{204}{504} \\\\ &=\frac{17}{42} \end{aligned}

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