A guitar manufacturer branch ships the guitar parts after its quality control (QC) system separates good parts from defective parts. Let A be event that a checked part passed quality control Let B be the event that a part is really good. The QC system is not perfect. The QC system is correct 90% of the time when the part is good, i.e. P(A|B)=0.9. The QC system is correct 75% of the time when the part is not good, i.e. P(Ac|Bc)=0.75. The market analysis shows that 90 % of shipped parts are good and there is no warranty claims for the parts, i.e. P(B)=0.9