Since the data follows a normal distribution, the 68-95-97 rule can be used to describe the number of people falling under N standard deviations from the mean. Since the standard deviation is 1, hemoglobin levels of 13 -15 g/dL contains 68% of the sample, or 136 people. This means the 32 people have less than 13 g/dL and 32 people have more than 15 g/dL.
