Uses information from the empirical rule. Visualize the normal distribution. The area under the curve from z = 0 to z =+1 is .34. The area from -1 to +1 is 68% per the empirical rule. This is the probability that z is greater than 0 but less than +1. The probability that z is greater than 0 is .50. Thus the probability of a z value larger than z = +1 is .50 - .34 = .16. This is the same as the probability of a value larger than one standard deviation above the mean. Remember that z = +1 is one standard deviation higher than the mean. What about z = -1? That is one standard deviation below the mean