describe the mean and variance using the probability distribution.
Bill Russ, a production manager at Ross Co., maintains full records on the number of times each machine breaks down as well as requires service during the week. Bill records display that the Puret grinder has required repair service according to the subsequent distribution
Number of Breakdowns per week

Weeks

Probability


0

20

0.333


1

20

0.333


2

10

0.167


3

10

0.167



60

1.000

totals

a) find out the arithmetic mean number of breakdowns per week.
b) find out the variance of the number of breakdowns per week.