Thread: Probability problem

A sample of 100 items is taken at random from a batch known to contain 40% defectives. What is the probability that the sample contains (i) at least 44 defectives (ii) exactly 44 defectives?

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Hi Sagarmte,
Presumably you have a random sample X_1, X_2, ... X_100 from a Bernoulli trials population (0 for failure; i.e. good item and 1 for success - bad item). The parameter is p = .4. Don't you then know the distribution of X_1+X_2+ ... X_100? Assuming you do, you can then answer your questions using this distribution.