3. Find the mean and the standard deviation for each of the following sets of data. For the calculations assume a), b) are populations, while c) and d) are samples. a X 1 2 3 4 5 6 f 2 6 11 15 8 b) Interval Frequency 1 to under 3 3 to under 5 5 to under 7 - UIC AN 7 to under 9 9 to under 11 C) Interval Frequency 20 to under 25 25 to under 30 6 30 to under 35 10 35 to under 40 2 40 to under 45 d) X 10 20 30 40 50 60 3 9 14 10 6 4