A sample consisting of 100 employees has been given a manual-dexterity test. Given the accompanying frequency distribution, determine the approximate mean and standard deviation for these data.
Data for Exercise 3.40
Score Number of Persons
5–under 15........... 7
15–under 25........... 9
25–under 35......... 12
35–under 45......... 14
45–under 55......... 13
55–under 65........... 9
65–under 75........... 8
75–under 85......... 11
85–under 95......... 10
95–under 105......... 7