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Mathematics · 2022 · 2 marks
CBSE 2022 · Region 4 · Set 1 · Q1
A bag contains 3 red and 4 white balls. Three balls are drawn at random, one-by-one without replacement from the bag. If the first ball drawn is red…
A bag contains $\displaystyle 3$ red and $\displaystyle 4$ white balls. Three balls are drawn at random, one-by-one without replacement from the bag. If the first ball drawn is red in colour, then find the probability that the remaining two balls drawn are also red in colour.
Marking-scheme solution
$\displaystyle A$ : First ball drawn is red$\displaystyle B$ : Remaining two balls are red$$P(B/A) = \frac{P(B \cap A)}{P(A)}$$$$= \frac{\dfrac{1}{35}}{\dfrac{3}{7}} = \frac{1}{15}$$
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CBSE Class 12 Mathematics past-paper question from the 2022 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.