The population 3, 4, 9, 14, and 20 has a mean of 10 and a standard deviation of 6. 356. The z- scores for each of the five data values are z3 = - 1. 101, z4 = - 0. 944, z9 = - 0. 157, z14 = 0. 629, and z20 = 1. 573. Find the standard deviation of the z-scores.