A Mercedes Benz mechanic, in determining whether to purchase a device of design A or design B, checks the times for completing a certain task on each device. Eight operators were used in the testing, with each operator using both device A and B in a randomized order. The times (in seconds) required to complete the task are given in the following tables.

Operator

B

1 32 30

2 40 39

3 42 42

4 26 23

5 35 36

6 29 27

7 45 41

8 22 21

a)At alpha level equal to 0.05; test to see if there is a significant difference between mean completion times.

b)What assumptions are necessary for this test?

c) Determine the 95% level of confidence interval for the difference between A and B