To find the mean and variance using the probability distribution.
Bill Russ, the production manager at Ross Co., maintains detailed records on number of times each machine breaks down and requires service all through the week. Bill records show that the Puret grinder has required repair service according to the following 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] calculate the arithmetic mean number of breakdowns per week.
[b] Calculate the variance of the number of breakdowns per week.