The number of days required per audit for 200 recent audits by Bell Accounting Group is shown in the relative frequency table below: 

Length of Audit (days)         Proportion of Audits

1……………………………………..            .39

2……………………………………..            .27

3……………………………………..            .17

4……………………………………..            .08

5……………………………………..            .05

6……………………………………..            .04

a. Compute the mean audit time. 

b. Determine the median audit time. 

c. Compute the variance and the standard deviation of the audit times.