2 First test for the mean: one sample and one set of measurements

We explain this first technique by means of an example. There is a “rule of thumb” in libraries that, on the average, there are 30 books per running shelf metre (for fully occupied shelves, of course). A sample of N=125 m of fully occupied shelves in my library gives me 125 numbers x1, x2, …, x125 (each being a number of books on 1 m of shelf) with average and standard deviation s. We only need and s here, e.g.