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Mathematics · 2025 · 3 marks
CBSE 2025 · Region 6 · Set 3 · Q31
Bag I contains 4 white and 5 black balls. Bag II contains 6 white and 7 black balls. A ball drawn randomly by from bag I is transferred to bag II and…
Bag I contains $\displaystyle 4$ white and $\displaystyle 5$ black balls. Bag II contains $\displaystyle 6$ white and $\displaystyle 7$ black balls. A ball drawn randomly by from bag I is transferred to bag II and then a ball is drawn randomly from bag II. Find the probability that the ball drawn is white.
Marking-scheme solution
$\displaystyle \mathrm{P}($ white ball transferred $\displaystyle )=\frac{4}{9}$, Probability( black ball transferred) $\displaystyle =\frac{5}{9}$
$\displaystyle \mathrm{P}($ white ball drawn from bag II $\displaystyle )=\frac{4}{9} \cdot \frac{7}{14}+\frac{5}{9} \cdot \frac{6}{14}$
\[=\frac{29}{63}
\]
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CBSE Class 12 Mathematics past-paper question from the 2025 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.