The following data represent the number of appointments made per 15-minute interval by telephone solicitation for a lawn-care company. Assume these are population data.

Number of

appointments Frequency

of occurrence

0 under 1 31

1 under 2 57

2 under 3 26

3 under 4 14

4 under 5 6

5 under 6 3

Calculate the standard deviation.

Keep 3 decimal places where necessary.