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40% of the buttons manufactured by a firm are found to be defective. In a random sample of six buttons, find the probability of getting.(i) exactly 4 defective buttons (ii) more than one defective button. |
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Answer» Let X be the number of buttons manufactured is a Binomial. Variate with parameters n = 6 and p = 40% = 0.4, so q = 1 – p = 0.6. Then the probability mass function is: p (x) = nCx px qn-x = 0, 1, 2 ……. n. = 6Cx (0.4)x (0.6)6-x ; x = 0, 1, 2 6. (i) P(exactly 4 defective buttons) = p(x = 4) = 6C4 (0.4)4 (0.6)6-4 = 15 × 0.0256 × 0.36 = 0.1382 (ii) P(more than 1 defective button) =p(x > 1) = 1 -p(x = 0) = 6C0 (0.4)0 (0.6)6-0 = 1.1. 0.466 = 0.0466. |
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