Two hundred employee travel expense reimbursement vouchers were led last year in the - finance department at Ramjac Corporation. Of these, 20 contained errors. A corporate auditor audits a sample of five vouchers. Let X be the number of incorrect vouchers in the sample.
(a) Justify the use of the binomial approximation.
(b) Find the probability that the sample contains no erroneous vouchers.
(c) Find the probability that the sample contains at least two erroneous vouchers.