The hours worked last week by 40 employees of a local clothing factory were as follows:
38 40 46 32 41 39 44 38 40 42 38 40 43 41
47 36 38 39 34 40 48 30 49 40 40 43 45 36
35 39 42 44 48 36 38 42 46 38 39 40
a. Calculate the mean and standard deviation for this data.
b. Now group the data into classes 30 - 33, 34 - 37, and so on. Calculate the mean and standard deviation using these groups. Examine any differences between the two sets of answers.