Cookies are made in a factory with an average mass of 22 grams and a standard deviation of 4 grams. some cookies are packed in a box. According to the manufacturer, the average mass of a cookie from at least 99% of the boxes is at least 20 grams. How many cookies should the manufacturer at least put in a box?
You can play around with Z table stuff at
http://davidmlane.com/hyperstat/z_table.html