Thirty percent of all telephones of a certain type are submi

Thirty percent of all telephones of a certain type are submitted for service while under warranty. Of these, 70% can be repaired, whereas the other 30% must be replaced with new units. If a company purchases ten of these telephones, what is the probability that exactly three will end up being replaced under warranty? (Round your answer to three decimal places.)

Solution

Pr(repair and replace)=P(replace/repair)*P(repair)

=0.30*0.30=0.09

Let, X=number of telephones which needs repair

S=a telephone needs repair and with replacement

P(X=3)=10C3*0.09^3*(1-0.09)^7

=0.045