6.2 A machine is operated so as to produce ball bearings having a mean

diameter of 0.55 cm and with a standard deviation of 0.01 cm. To

determine whether the machine is in proper working order a sample of six

ball bearings is taken every half-hour and the mean diameter of the six is

computed.

(a) Design a decision rule whereby one can be fairly certain that the ball

bearings constantly meet the requirements.

(b) Show how to represent the decision rule graphically.

(c) How could even better control of the process be maintained?