15. A sandwich shop advertises that it delivers 90% of its orders within 30 minutes. You select an SRS of 50 of the orders delivered in the past week for an audit. Let p = the proportion of orders delivered in the last week that were delivered within 30 minutes. (a) Calculate the mean and the standard deviation of the sampling distribution of p . (b) Interpret the standard deviation from part (a). (c) Would it be appropriate to use a normal distribution to model the sampling distribution of p ? Justify your