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 and be two urns such that contains 3 white and 2 red balls and contains only 1 white ball. A fair coin is tossed. If head appears then 1 ball is drawn at random from and put into . However, if tail appears then 2 balls are drawn at random from and put into . Now, 1 ball is drawn at random from .Question:
The probability of the drawn ball from being white is
Options
- A
- B
- C
- D
Correct answer
B.
Step-by-step solution
Now, probability of the drawn ball from being white is
\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}