A pizza delivery person was interested in knowing how she spends her time and what her actual hourly earnings are, so she recorded all of her deliveries and tips and how she spent every minute of her time over three shifts, on one Friday night and two Saturday nights. She discusses the results, and much more, on ‘‘Diary of a Pizza Girl” on the Slice website. Some of these data are available in PizzaGirl. The average tip for pizza deliveries on the nights sampled is x̅ = $3.04. If we want to use this sample mean to estimate the average tip for all deliveries, the margin of error is $0.86. Find an interval estimate for the average tip for all pizza deliveries she makes. What do we have to assume about the sample in order for this point estimate and interval estimate to be valid?