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A box contains certain number of balls of Black, White and Pink Colors in the ratio 5 : 9 : 20. If two balls are drawn randomly and probability of getting both the balls as Pink is \(\frac{390}{1139}\), then find the number of Black Balls. |
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2 |
Let the number of Black, White and Pink balls are 5X,9X and 20X respectively. Total Number of Balls = 34X Probability of Getting two pink Balls = \(\frac{^{20R} \mathrm{ C }_2}{^{34R} \mathrm{ C }_2}\) = \(\frac{390}{1139}\) ⇒ \(\frac{20R\;×\;(20R\;-\;1)}{34R\;×\;(34R\;-\;1)}\) = \(\frac{390}{1139}\) ⇒ On solving, R = 2Number of Black Balls ⇒ R = 2 Hence, option A is correct. |
