Pulse Rates of Adults Assume that adults have pulse rates (beats per minute) with a mean of 72.9 and a standard deviation of 12.3 (based on data from the National Health Examination). When this exercise question was written, the author's pulse rate was 48.

a. What is the difference between the author's pulse rate and the mean?

b. How many standard deviations is that [the difference found in part (a)]?

c. Convert a pulse rate of 48 to a z score.

d. If we consider "usual" pulse rates to be those that convert to z scores between 22 and 2, is a pulse rate of 48 usual or unusual? Can you explain why a pulse rate might be unusually low? (The reason for this low pulse rate is not that statistics textbook authors are usually in a state that could loosely be described as comatose.)