In a problem involving data that is normally distributed, the Z-score is
how many standard deviations from the mean that a sample data value
lies. For example, if the standard deviation is 10 and the mean is 20,
then a data value of 25 is 5 units from the mean and 5/10, which is 1/2
standard deviation away from the mean. The Z-score is then 0.5.