A scientist studying babies born prematurely would like to obtain an estimate for the mean birth weight, , of babies born during the 24th week of the gestation period. She plans to select a random sample of birth weights of such babies and use the mean of the sample to estimate . Assuming that the population of birth weights of babies born during the th week has a standard deviation of pounds, what is the minimum sample size needed for the scientist to be confident that her estimate is within pounds of μ?