The accounting department wants to audit travel expense forms. It is concerned about the proportion of cheques issued for travel expenses that do not have adequate documentation.

a) Determine how many travel expense forms must be checked to determine the true proportion of expense forms without adequate documentation, to within 4% at a 95% level of confidence.

b) A sample of 500 forms was audited and it was revealed that 15% did not have proper documentation. Construct a 99% confidence interval for the true proportion of travel expense forms that lack proper documentation.