The Bell Curve
Normal Distribution – shows data that vary randomly from the mean.
Normal Curve – The pattern the data form is a bell-shaped curve.
The Standard Normal Bell Curve
68% of the data fall within one standard deviation of the mean
95% of the data fall within two standard deviations of the mean
Using the Standard Normal Curve
Ex 1) A survey of the employees of XYZ Corporation found that the
mean of the morning commute times to work was 18 minutes. The
standard deviation was 4 minutes. Sketch a normal curve showing the
commute times at one, two, and three standard deviations from the mean.
1) What values are one standard
deviation from the mean?
2) What percent of the data can you
expect to find between 18 and 22
minutes?
3) Of 124 commuters, how many could
you expect to be driving between 22
and 25 minutes to work?