The following table gives the number of finished articles turned out per day be different number of workers in a factors. Find the standard deviation of the daily output of finished articles. Find the variance and standard deviation of the following frequency distribution:
Number of article:, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27
No. of workers:, 3, 7, 11, 14, 18, 17, 13, 8, 5, 4