Suppose that only 0.1% of all computers of a certain type experience CPU failure

Question

Suppose that only 0.1% of all computers of a certain type experience CPU failure during the warranty period. Consider a sample of 9,000 computers. What are the expected value and standard deviation of the number of computers in the sample that have the defect? (Round your standard deviation to two decimal places.) expected value 9 computers standard deviation 3 computers What is the (approximate) probability that more than 13 sampled computers have the defect? () .587 What is the (approximate) probability that no sampled computers have the defect? (Round your answer to five decimal places.) .00012

Explanation / Answer

probabilty of defect =0.001

here expected value =np =9000*0.001 =9

and std deviation =(np(1-p))1/2 =(9000*0.001(1-0.001))1/2 =2.9985 ~3

b) here P(X>13) =1-P(X<=13) =1-P(Z<(13.25-9)/3)) =1-P(Z<1.416) =1-0.926 =0.074

probabilty that no sampled computers have the defect =(1-0.001)9000 =0.00012

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