The level of nitrogen oxides (NOX) in the exhaust of a particular car model varies with mean 0.7 grams per mile and standard deviation 0.16 grams per mile .
(a) What sample size is needed so that the standard deviation of the sampling distribution is 0.01 grams per mile ?
You can play around with Z table stuff at
http://davidmlane.com/hyperstat/z_table.html