we need to find the probability of bad sound cards.
we are having 1000 computers so 1000 sound card will be there.
manager found that 4 sounds are defective out of 1000 sound cards.
[tex] P(D) [/tex] of defective sound cards=[tex] n(D)/n(s)=4/1000=0.004 [/tex]
we know that 1 is the total probability.out of 0.004 is the failure.