Question

Ridge counts on fingerprints are approx. normally distributed, with a mean of about 140 and standard deviation of 50. What does the 68-99-95.7% Rule tell us about ridge counts on fingerprints?

Answer 1

one sec

Answer 2

Note that the range "within one standard deviation of the mean" is highlighted in green. The area under the curve over this range is the relative frequency of observations in the range. That is, 0.68 = 68% of the observations fall within one standard deviation of the mean, or, 68% of the observations are between (mu - sigma) and (mu + sigma).

Below the axis, in red, is another set of numbers. These numbers are simply measures of standard deviations from the mean. In working with the variable X we will often find it necessary to convert into units of standard deviations from the mean. When the variable is measured this way, the letter Z is commonly used.