8.37 Shipping the orders on time.

As part of a quality improvement program, your mail-order company is studying the process of filling customer orders. According to company standards, an order is shipped on time if it is sent within two working days of the time it is received. You select an SRS of 100 of the 6000 orders received in the past month for an audit. The audit reveals that 87 of these orders were shipped on time. Find a 95% confidence interval for the true proportion of the month's orders that were shipped on time.