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प्रश्न
Two balls are drawn at random with replacement from a box containing 10 black and 8 red balls. Find the probability that one of them is black and other is red.
उत्तर
\[\text{ Given : Box } = \left( 10B + 8R \right) \text{ balls } \]
\[ P\left( \text{ one is red and one is black } \right) = P\left( \text{ first red and second black } \right) + P\left( \text{ first red and second black } \right)\]
\[ = \frac{8}{'18} \times \frac{10}{18} + \frac{10}{18} \times \frac{8}{18}\]
\[ = \frac{80}{324} + \frac{80}{324}\]
\[ = \frac{40}{81}\]
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