Answer:
a) 4.9 % of all parts is defective or 0.049 of the total parts.
b) 0.5102 is the probability that the defective part was supplied by S1
Step-by-step explanation:
N is the total number of parts from supplier S1, S2 and S3.
N1 = 0.5*N is the total number of part supplied by S1
N2 = 0.2*N is the total number of part supplied by S2
N3 = 0.3*N is the total number of part supplied by S3
a) if Nd1 is the number of defective parts from supplier S1, Nd2 is the number of defective parts from supplier S2 and Nd3 is the number of defective parts from supplier S3, the the total defective parts Nd is:
Nd = Nd1 + Nd2 + Nd3, where
Nd1 = 0.05*N1 = 0.05*0.5*N = 0.025*N,
Nd2 = 0.03*N2 = 0.03*0.2*N = 0.006*N,
Nd3 = 0.06*N3 = 0.06*0.3*N = 0.018*N,
Then Nd = Nd1 + Nd2 + Nd3 = 0.049*N, so Nd/N = 0.049
b)
for the last expression I used the Bayes tehorem.
is the probability that occur S1 given that d (defective) is true. This a conditional probability.
see at https://en.wikipedia.org/wiki/Bayes%27_theorem
