1 . A machine produces metal rods used in an automobile suspension system. A random sample of 15 rods is selected and the diameter is measured. The resulting data (in millimeters) is tabulated row wise as follows:

8.24 8.25 8.20 8.23 8.24

8.21 8.26 8.26 8.20 8.25

8.23 8.23 8.19 8.28 8.24

a) Conduct a normality test to check whether the data is distributed normally.

b) Find a 95% two-sided confidence interval on mean rod diameter.

c) The vendor claims that he can produce rods of mean diameter 8.1 mm. Verify his claim with a level of significance of 0.05.