Step-by-step explanation:
a probability is always the ratio
desired cases / totally possible cases
a)
totally possible cases of system A : 300
"desired" (defect) cases of system A : 300 - 291 = 9
totally possible cases of system B : 400
"desired" (defect) cases of system B : 400 - 392 = 8
the probability of creating a defective product in A is
9/300 = 3/100 = 0.03
the probabilty of creating a defective product in B is
8/400 = 2/100 = 0.02
b)
exactly one of the 2 products is qualified.
so, either the one of A is qualified and the one of B is defective, or the one of B is qualified and the one of A is defective.
independent "and" relations are expressed as multiplications of the individual events.
exclusive "or" relations are expressed as summary of the individual events.
so, in our case
the probability of a qualified product in A is
291/300 = 97/100 = 0.97
the probability of a qualified product in B is
392/400 = 98/100 = 0.98
and the combined probability is
0.97×0.02 + 0.98×0.03 = 0.0488