For a population with mean of 100 and population standard deviation of 20, the X value corresponding to, z = 1.50 is ______? Solution ANSWER: Probability of single score between 80 and 120 = 68.2% [within +/-1 standard deviation] Probability of single score between 60 and 140 = 95.5% [within +/2 standard deviations] Probability of single score between 40 and 160 = 99.7% [within +/3 standard deviations].