Rachel measured the lengths of a random sample of 100 screws. The mean length was 2.9 inches, and the population standard deviation is 0.1 inch. z equals fraction numerator x with bar on top minus mu over denominator begin display style bevelled fraction numerator sigma over denominator square root of n end fraction end style end fraction To see if the batch of screws has a significantly different mean length from 3 inches, what would the value of the z-test statistic be