# statistics

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**HELP ME** on
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A manufacturer makes two models of an item: model A which accounts for 70% of unit sales, and model B which accounts for 30% of unit sales. Because of defects, the manufacturer has to replace (or exchange) 4% of its model A and 17% of its model B.

Question 9 : If a unit is selected at random from the combined output, what is the probability that it will be defective?