Standard deviation tells you about the variation within a sample.
The mean value tells you the average of the values collected in a sample.
It can be used to tell if there's variation between samples.. if the mean is vastly different, then there's a lot of variation between the two samples.
Most samples give you a bell-shaped graph - this is called a normal distribution.
The standard deviation tells you how much the values in a single sample vary.
Small standard deviation = little variation, and vice versa.
Good luck on your exams!
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