Question 4

A random sample of 49 ball-bearings made by a new machine was taken over the first day of testing the new machine. The ball-bearings in the sample had a mean diameter of 0.824 mm with a standard deviation of 0.042 mm. The mean from older machines of the same type had been found to be in the range 0.820 0.01.

(a) What is the 95% confidence interval for the mean diameter from the new machine?

(b) With approximately what degree of confidence can we say that the mean diameter from the new

machine is 0.824 0.01?

(c) Howwouldyourresultsin(a)changeiftherandomsamplehadbeenof20ball-bearings?