There is a data set consisting of the aluminum contents of 26 bihourly samples of recycled PET plastic from a recycling facility. Those 26 measurements have y(bar)= 142.7 ppm and s= 98.2 ppm. Use these facts to respond to the following. (Assume that n=26 is large enough to permit the use of large-sample formulas in this case.)
1) Suppose that in order to monitor for possible process changes, future samples of PET will be taken. If it is desirable to estimate the mean aluminium content with +- 20 ppm precision and 90% confidence, what future sample size do you reccomend?