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Mathematics · 2024 · 3 marks
CBSE 2024 · Region 5 · Set 2 · Q31
Bag I contains 3 red and 4 black balls, Bag II contains 5 red and 2 black balls. Two balls are transferred at random from Bag I to Bag II and then a…
Bag I contains $\displaystyle 3$ red and $\displaystyle 4$ black balls, Bag II contains $\displaystyle 5$ red and $\displaystyle 2$ black balls. Two balls are transferred at random from Bag I to Bag II and then a ball is drawn at random from Bag II. Find the probability that the drawn ball is red in colour.
Marking-scheme solution
E1: Two Balls transferred from Bag I are Red.
E2: Two Balls transferred from Bag I are Black.
E3: Two Balls transferred from Bag I are Red and Black.
A: Ball drawn from Bag II is Red
$$\begin{gathered}
\mathbf{P}\left(\mathrm{E}_{1}\right)=\frac{1}{7}, \mathbf{P}\left(\mathrm{E}_{2}\right)=\frac{2}{7}, \mathbf{P}\left(\mathrm{E}_{3}\right)=\frac{4}{7}, \mathbf{P}\left(\mathrm{~A} \mid \mathrm{E}_{1}\right)=\frac{7}{9}, \mathbf{P}\left(\mathrm{~A} \mid \mathrm{E}_{2}\right)=\frac{5}{9}, \mathbf{P}\left(\mathrm{~A} \mid \mathrm{E}_{3}\right)=\frac{6}{9} \\
\mathbf{P}(\mathrm{~A})=\frac{1}{7} \cdot \frac{7}{9}+\frac{2}{7} \cdot \frac{5}{9}+\frac{4}{7} \cdot \frac{6}{9}=\frac{41}{63}
\end{gathered}
$$
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CBSE Class 12 Mathematics past-paper question from the 2024 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.