Data 2.12 on page 119 describes information from a sample of 157 restaurant bills collected at the First Crush bistro. The data is available in RestaurantTips. Two intervals are given below for the average tip left at a restaurant; one is a 90% confidence interval and one is a 99% confidence interval.
Interval A: 3.55 to 4.15

Interval B: 3.35 to 4.35
(a) Which one is the 90% confidence interval? Which one is the 99% confidence interval?
(b) One waitress generally waits on 20 tables in an average shift. Give a range for her expected daily tip revenue, using both 90% and 99% confidence. Interpret your results.

Data 2.12 on page 119

The owner of a bistro called First Crush in Potsdam, New York, is interested in studying the tipping patterns of its patrons. He collected restaurant bills over a two-week period that he believes provide a good sample of his customers. The data from 157 bills are stored in RestaurantTips and include the amount of the bill, size of the tip, percentage tip, number of customers in the group, whether or not a credit card was used, day of the week, and a coded identity of the server.