How to find the sample size based on normal distribution.
A processor of carrots grazes the green top off each carrot washes the carrots, as well as inserts six to a package. Twenty packages are introduced in a box for shipment. To test the weight of the boxes a few were checked. The mean weight was 20.4 pounds the standard deviation 0.5 pounds. How many boxes should the processor sample to be 95 percent confident that the sample mean doesn't differ from the population mean by more than 0.2 pounds?