Variance and Standard Deviation
1) Good, to the point, explanation: http://www.mathsisfun.com/data/standard-deviation.html
2) Video: https://www.khanacademy.org/math/probability/descriptive-statistics/variance_std_deviation/v/range--variance-and-standard-deviation-as-measures-of-dispersion
3) Standard Deviation in just 6 steps: http://www.wikihow.com/Calculate-Standard-Deviation
4) Using EXCEL to calculate the standard deviation: http://www.gifted.uconn.edu/siegle/research/normal/stdexcel.htm
2) Video: https://www.khanacademy.org/math/probability/descriptive-statistics/variance_std_deviation/v/range--variance-and-standard-deviation-as-measures-of-dispersion
3) Standard Deviation in just 6 steps: http://www.wikihow.com/Calculate-Standard-Deviation
4) Using EXCEL to calculate the standard deviation: http://www.gifted.uconn.edu/siegle/research/normal/stdexcel.htm