Chapter 3: Averages and Variation Section 3: Mean and Standard Deviation of Grouped Data

Sample mean for a frequency distribution x = midpoint of class f = frequency n =

Sample standard deviation for a frequency distribution x = midpoint of class f = frequency n =

Example Class f Midpoint (x) 0 – 2 4 1 - 9.2 84.64 338.56 3 – 5 3 12 -6.2 38.44 115.32 6 – 8 8 7 56 -3.2 10.24 81.92 9 – 11 15 10 150 -0.2 0.04 0.60 12 – 14 13 169 2.8 7.84 101.92 15 – 17 5 16 80 5.8 33.64 168.2 18 – 20 2 19 38 8.8 77.44 154.88   50 509 961.40

Example (Cont)