The ratio of the number of lathes, drill presses, grinders and planers in a factory is 9: 3: 2: 1, and the ratio of the probabilities they need to be repaired in a certain period of time is 1: 2: 3
A4 = {a machine for the planer}, P (A4) =
A3 = {a machine for the grinder}, P (A3) =
A2 = {a machine for the drilling machine}, P (A2) =
Set A1 = {a machine for the lathe}, P (A1) =
