a. A statistics practitioner would like to estimate a population

a. A statistics practitioner would like to estimate a population mean to within 50 units with 99% confidence given that the population standard deviation is 250. What sample size should be used?,b. Re-do part (a) changing the standard deviation to 50.,c. Re-do part (a) using a 95% confidence level.,d. Re-do part (a) wherein we wish to estimate the population mean to within 10 units.