Example: The data represent the number of miles that 20 runners ran during one week. Find the variance and the standard deviation for the frecuency distribution of the data. 23 8383833 Class Frequency Midpoint 5.5-10.5 1 10.5-15.5 15.5-20.5 20.5-25.5 13 18 235432 25.5-30.5 30.5-35.5 4 28 35.5-40.5