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JEE Advanced 2011Paper 1
Exam
JEE Advanced
Year
2011
Paper
Paper 1
Subject
Mathematics
Chapter
Probability

JEE Advanced 2011 · Paper 1 · Mathematics · Probability

Paragraph: Let U_1 and U_2 be two urns such that U_1 contains 3...

Paragraph: Let U1U_1 and U2U_2 be two urns such that U1U_1 contains 3 white and 2 red balls and U2U_2 contains only 1 white ball. A fair coin is tossed. If head appears then 1 ball is drawn at random from U1U_1 and put into U2U_2. However, if tail appears then 2 balls are drawn at random from U1U_1 and put into U2U_2. Now, 1 ball is drawn at random from U2U_2.Question: The probability of the drawn ball from U2U_2 being white is

Options

  1. A1330\frac{13}{30}
  2. B2330\frac{23}{30}
  3. C1930\frac{19}{30}
  4. D1130\frac{11}{30}

Correct answer

B. 2330\frac{23}{30}

Step-by-step solution

Now, probability of the drawn ball from V2\mathrm{V}_2 being white is ⇒P (white/ V2 ) \Rightarrow P \text{ (white/ } V_2 \text{ ) }\begin{aligned} & \left.\Rightarrow P \text{ (white/ } V_2\right) \\ & =P(H) \cdot\left\{\frac{{ }^3 C_1}{{ }^5 C_1} \times \frac{{ }^2 C_1}{{ }^2 C_1}+\frac{{ }^2 C_1}{{ }^5 C_1} \times \frac{{ }^1 C_1}{{ }^2 C_1}\right\} \\ & +P(T)\left\{\frac{{ }^3 C_2}{{ }^5 C_2} \times \frac{{ }^3 C_2}{{ }^3 C_2}+\frac{{ }^2 C_2}{{ }^5 C_2} \times \frac{{ }^1 C_1}{{ }^3 C_2}\right. \\ & \left.+\frac{{ }^3 C_1 \cdot{ }^2 C_1}{{ }^5 C_2} \times \frac{{ }^2 C_1}{{ }^3 C_2}\right\} \\ & \text{ Now, } P\left(\text{ white } / V_2\right)=\frac{1}{2}\left\{\frac{3}{5} \times 1+\frac{2}{5} \times \frac{1}{2}\right\} \\ & +\frac{1}{2}\left\{\frac{3}{10} \times 1+\frac{1}{10} \times \frac{1}{3}+\frac{6}{10} \times \frac{2}{3}\right\}=\frac{23}{30} \\ & \end{aligned}
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