In this video Paul Andersen explains the importance of standard deviation. He starts with a discussion of normal distribution and how the standard deviation measures the average distance from the mean, or the "spread" of data. He then shows you how to calculate standard deviation by hand using the formula. He finally shows you how to calculate the standard deviation using a spreadsheet.
The calculated standard deviation is 2.7.
Intro Music Atribution
Link to sound: http://www.freesound.org/people/CosmicD/sounds/72556/
Creative Commons Atribution License