Ex 13.5, 13 - Chapter 13 Class 12 Probability

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Ex 13.5, 13 It is known that 10% of certain articles manufactured are defective. What is the probability that in a random sample of 12 such articles, 9 are defective? In each of the following, choose the correct answer: Let X : be the number of defective articles Picking articles is a Bernoulli trial So, X has binomial distribution P(X = x) = nCx n = number of articles = 12 p = Probability of getting defective articles = 10% = 10 100 = 1 10 q = 1 p = 1 1 10 = 9 10 Hence, P(X = x) = 12Cx We need to find Probability of getting 9 defective articles out of 12 i.e. P(X = 9) P(X = 9) = 12C9 1 10 9 9 10 12 9 = 12 ! 12 9 ! 9 ! 1 10 9 9 10 3 = 12 11 10 9 ! 3 ! 9 ! 1 10 9 9 10 3 = 12 11 10 3 2 1 1 10 9 9 10 3 = 2 11 10 8 9 3 10 3 = 22