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Mathematics · 2026 · 3 marks
CBSE 2026 · Region 4 · Set 1 · Q30
A bag contains 30 balls out of which 'm' number of balls are blue in colour. (i) Find the probability that a ball drawn at random from the bag is not…
A bag contains $\displaystyle 30$ balls out of which 'm' number of balls are blue in colour.
(i)
Find the probability that a ball drawn at random from the bag is not blue.
(ii)
If $\displaystyle 6$ more blue balls are added in the bag, then the probability of drawing a blue ball will be $\displaystyle \frac{5}{4}$ times the probability of drawing a blue ball in the first case. Find the value of m.
Marking-scheme solution
(i)
P (ball drawn is not blue) \(\displaystyle =\frac{30-m}{30}\) or \(\displaystyle 1-\frac{m}{30}\)
(ii)
Total number of balls now = $\displaystyle 36$
Number of blue balls now \(\displaystyle =\mathrm{m}+6\)
\[\mathrm{P}(\text { ball drawn is blue })=\frac{m+6}{36}
\]
According to question, \(\displaystyle \frac{m+6}{36}=\frac{5}{4} \times \frac{m}{30}\)
\[\Longrightarrow \mathrm{m}=12
\]
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CBSE Class 10 Mathematics past-paper question from the 2026 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.