Statistics homework HELP! number 2?

At a small metal fabrication company, steel rods of a particular type cut to length have lengths with standard deviation 0.005 in. In an effort to determine the mean length produced using the current setup of the jig, a sample of rods is to be taken and their lengths measured, with the intention of using the value of X-bar as an estimate of �. Approximate the probabilities that X-bar is within .0005 in. of � for samples of size n = 50, 100 and 400.