So lets do it like this: z = (X-Mean)/SD z1 = (8-12)/2 = - 2 z2 = (16-12)/2 = + 2 According to the Empirical Rule 68-95-99.7 Mean more or less 2SD covers 95% of the values So the percentage of data points falling between 8 and 16 = 95% I hope this can help
