PMP Exam: Statistics for Normal and Cumulative Distributions
PMPs (project management professionals) often apply basic statistics to their projects. For the PMP certification exam, here’s what you need to know when dealing with normal and cumulative distributions:
Equations are based on a normal distribution. In a normal distribution, keep the following in mind:

68.3% of the data points fall within one standard deviation.

95.5% of the data points fall within two standard deviations.

99.7% of the data points fall within three standard deviations.
If you’re looking at a normal curve and need a cumulative distribution, you should remember these values:

0.15% of the data points fall between 0 and –3 from the mean.

2.25% of the data points fall between 0 and –2 from the mean.

16% of the data points fall between 0 and –1 from the mean.

84% of the data points fall between 0 and +1 from the mean.

97.75% of the data points fall between 0 and +2 from the mean

99.85% of the data points fall between 0 and +3 from the mean.