Companies MPL, QS and RobotS supply machine parts in a 5:3:2 ratio respectively. 0.2% of the parts from MPL are defective. 0.1% are defective from QS and 0.5% are defective from RobotS.
For two machine parts chosen at random, calculate the probability that:
a) Both are supplied from MPL and both are defective.
b) Both supplied by one of the other companies and found to be defective.
(Being stupid I know, but blanked on this.)