It is known that the computer disks produced by a company are defective with probability 0.02 independently of each other. Disks are sold in packs of 10. A money back guarantee is offered if a pack contains more than 1 defective disk. What is the probability of sales result in the customers getting their money back?

Question

It is known that the computer disks produced by a company are defective with probability 0.02 independently of each other.  Disks are sold in packs of 10. A money back guarantee is offered if a pack contains more than 1 defective disk. What is the probability of sales result in the customers getting their money back?

anonymous · Answer

Probability of more than one [P(>1)] is one minus the probability of none or of one. 1 - P(0) - P(1) 

Probability of none is P(0) = (0.98)^10 = 0.817

Get probability of one, P(1) from binomial distribution.