The following are number of mistakes made on five occasions by word processor operators setting a technical report. Operator 1 10 13 9 11 12
Operator 2 11 13 8 16 12
Operator 3 10 15 13 11 15
Operator 4 15 7 11 12 9

Required:
a. Perform an analysis of variance and decide at the 0.01 level of significance whether the differences among the four-sample means can be attributed to chance.
b. State the null and alternative hypothesis.