Te shelf life (duration until the expiration date in months) of certain ointment is known to have a normal distribution. a sample of size 120 tubes of ointment gives x = 36.1 and s = 3.7.

a. construct a 95% confdence interval of the population mean shelf life.

b. suppose a researcher believed before the experiment that 4 σ = . what would be the required sample size to estimate the population mean to be within 0.5 month with 99% confdence?