A random sample of 500 receipts was taken from a population with an unknown proportion of errors. If the computed confidence interval for the true proportion of receipts that contain an error is (4.22%,10.18%), answer the following questions:
(a) How many out of the sample of 500 was found to contain an error? [Hint: What point is at the center of the confidence interval?]
(b) Approximate the level of confidence that was used to generate this interval.
(c) How large a sample is needed to reduce the margin of error to at most 0.01 (or 1%)? Be conservative by not assuming the sample proportion (obtained from the sample of 500) as the reasonable guess for p. Use the confidence level you found in part (b).