Glen's Mufflers and Exhaust has been experiencing a steady growth in sales. The following grouped data show the frequencies of daily sales volume (in hundreds of dollars):

Daily Sales Number of Days

.25 and under 1 3

1 and under 1.75 9

1.75 and under 2.5 10

2.5 and under 3.25 4

3.25 and under 4.0 2

4.0 and under 4.75 12

4.75 and under 5.5 6

5.5 and under 6.25 1

6.25 and under 7 3

7.0 and under 7.75 2

a) Calculate the mean daily sales

b)Calculate the variance and standard deviation of the daily sales.

Could you please show me how to work this step by step?