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Question -

There are 5% defective items in a large bulk of items. What is the probability that a sample of 10 items will include not more than one defective item?



Answer -

Let there be x numberof defective items in a sample of ten items drawn successively.

Now, as we can seethat the drawing of the items is done with replacement. Thus, the trials areBernoulli trials.

Now, probability ofgetting a defective item, p = 5/100 = 1/20

Thus, q = 1 – 1/20 =19/20

 We can say thatx has a binomial distribution, where n = 10 and p = 1/20

Thus, P(X = x) = nCqn-x px,where x = 0, 1, 2 …n

Probability of gettingnot more than one defective item = P(X ≤1)

= P(X = 0) + P(X = 1)

10C0 (19/20)10(1/20)0 +10C1 (19/20)9(1/20)1

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