find standard deviation

Find the standard deviation, s, of sample data summarized in the frequency distribution table given below by using the formula below, where x represents the class midpoint, f represents the class frequency, and n represents the total number of sample values. Also, compare the computed standard deviation to the standard deviation obtained from the original list of data values, 9.0. " [ E (f . x 2 ) ] - [ [ (. x ) ]2 S = n(n -1) Interval 20-26 27-33 34-40 41-47 48-54 55-61 Frequency N Standard deviation = (Round to one decimal place as needed.)