Among all the 200 transactions carried out in the last month, the owner of the Crmerie du Nord randomly selected 20 invoices. The mean of these 20 bills is $8.72 and the standard deviation is $2.13.

Question 11 What is the point estimate of the population mean?

Question 12 The owner claims that regardless of the sample (of 20 invoices) he takes, in 95% of cases, he will obtain an average between $7.72 and $9.72. Is he right? Explain.

Question 13 Determine the confidence interval for the population mean with an 80% confidence level.

Question 14 If the sample taken had been 40 invoices, would your answers have been different? Explain.

Question 15 Assuming the sample size and standard deviation remain the same (n=20 and standard deviation=2.13), what would have been the statistical margin of error for a confidence level of 90 %?