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Probability
RD Sharma
CBSE
Grade 10

Question:

A box contains $90$ discs numbered from $1$ to $90$. If one disc is drawn at random from the box, the probability that it bears a two-digit number is:
(a) $\dfrac{9}{10}$
(b) $\dfrac{1}{10}$
(c) $\dfrac{81}{90}$
(d) $\dfrac{8}{9}$

Step-by-Step Solution

Key Concept: Single-digit numbers: $1$ to $9$ (9 numbers). Two-digit numbers: $10$ to $90$ ($81$ numbers). $P = \dfrac{81}{90} = \dfrac{9}{10}$.
$P = 81/90 = 9/10$. [1.0 Mark]

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🎯 Official CBSE Marking Scheme:
Evaluating $9/10$: 1.0 Mark

Correct Answer: $\dfrac{9}{10}$
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