Mean, standard deviation, mwdian

Question

The credit manager of an organization carried out a study to determine the length of time that the customers take to pay their invoices and obtainer the following result

Days taken.            No. Of customers

5-9.                          4

10-14.                          10

15-19.                          17

20-24.                           20

25-29.                           22

30-34.                          16

35-39.                           8

40-44.                          3

Find:

1)Average days taken to settle the debt

2) Standard deviation

3)Median