A manufacturer makes two models of an item: model I, which accounts for 80% of unit sales, and model II, which accounts for 20% of unit sales. Because of defects, the manufacturer has to replace (or exchange) 10% of its model I and 18% of its model II. If a model is selected at random, find the probability that it will be defective. The answer is .116, I just can't figure out how to work out the problem. Can anyone please help?

Question

A manufacturer makes two models of an item: model I, which accounts for 80% of unit sales, and model II, which accounts for 20% of unit sales.  Because of defects, the manufacturer has to replace (or exchange) 10% of its model I and 18% of its model II.  If a model is selected at random, find the probability that it will be defective.  The answer is .116, I just can't figure out how to work out the problem.  Can anyone please help?

economyst · Accepted Answer

.80*.10 + .20*.18 = .116