The waiting time to place an order in a fast-food restaurant is normally distributed with unknown population standard deviation. The sample mean and sample standard deviation are 5.1 minutes and 1.5 minutes from a sample of 25 orders. What is the 90% confidence interval estimate of the population mean waiting time to place an order? [Hints: when the population standard deviation is known, the confidence interval estimate is X + Za/2 When the population standard deviation is unknown, the confidence interval estimate is X + ta/2 Vn. The following table can be used: Degree of % Confidence Interval freedom to/2 0.1 90 24 1.711 0.05 95 24 2.064 0.01 99 24 2.797