Surveyed 45 hard drives w/ a max error est of 28,how many include in new sample to reduce max error est to 7?

we know that z * sx is going to be a relative constant here. the z score should not change if we are looking for the same size confidence interval, nor should the standard deviation change that much.





we know (z*sx) / sqrt(45) = 28





so z*sx = 28sqrt(45)











n for the larger sample is:





n = (28 * sqrt(45) / 7)^2





n = 720 samples