Several drugs are used to treat diabetes. A sales specialist for a leading pharmaceutical company randomly sampled the records of 10 sales districts to estimate the number of new prescriptions that had been written during a particular month for her company's new diabetes drug. The numbers of new prescriptions were as follows:
210, 240, 190, 275, 290, 265, 312, 284, 261, 243
- a. Find a 90% confidence interval for the average number of new prescriptions written for this new drug among all the sales districts.
- b. Assuming that the confidence level remains constant, what sample size is needed to reduce by half the margin of error of the confidence interval in part (a)?