a) A machine is set to produce disc plates with a mean diameter of 14 mm. A sample of 8 discs gave a mean diameter, ?̅ = 14.9 mm and a standard deviation, s = 1.33 mm. A test was carried out at the 5%...

a) A machine is set to produce disc plates with a mean diameter of 14 mm. A sample of 8 discs
gave a mean diameter, ?̅ = 14.9 mm and a standard deviation, s = 1.33 mm. A test was
carried out at the 5% level of significance to determine whether the machine is in good
working order. Assume that the diameter of the disc follows a normal distribution.

ii. State, with reasons, whether a t-test or a z-test will be appropriate.