Forty cities provided information on vacancy rates (in percent) for local apartments in the following frequency distribution.

Vacancy Rate (in percent) Frequency

0 up to 3 10

3 up to 6 6

6 up to 9 9

9 up to 12 5

12 up to 15 10

a.Calculate the average vacancy rate.(Round your answer to 4 decimal places.)

b.Calculate the variance and the standard deviation for this sample.(Round intermediate calculations to at least 4 decimal places and final answers to 2 decimal places.)