A machine produces a stream of parts each of which is either

A machine produces a stream of parts, each of which is either good or defective. Quality is monitored by taking a sample of parts from the production line. How many defective parts will there be in a sample of 12, if there is one chance in 10 that a particular part is defective? Find the average number Y of defective s among the 12, and standard deviation.

Solution

given

no. of samples n=12

chance that a particular part is defective is 1/10

let D denotes no of defectives

so D follows bionomial distribution with n=12 p=0.1

so

Y =E(D) =12*0.1 =1.2

varience =12*0.9*0.1 =1.08

then standerd deviation =1.04