A sample of 25 patients in a doctor's office showed that they had to wait an average of 35 minutes with astandard deviation of 10 minutes before they could see the doctor. Provide a 98% confidence interval estimatefor the average waiting time of all the patients who visit this doctor. Assume the population of waiting times isnormally distributed.7. Below you are given ages that were obtained by taking a random sample of 9 undergraduate students.192223192122192321Use Excel to determine an interval estimate for the mean of the population at a 99% confidence level.Interpret your results.8. The manager of a department store wants to determine what proportion of people who enter the store use thestore's credit card for their purchases. What size sample should he take so that at 99% confidence the errorwill not be more than 8%?9.The manager of Hudson Auto Repair wants to advertise one price for an engine tune-up, with parts included. Beforehe decides the price to advertise, he needs a good estimate of the average cost of tune-up parts. A sample of20 customer invoices for tune-ups has been taken and the costs of parts, rounded to the nearest dollar, arelisted below.