A shipment of 12 microwave ovens contains 3 defective units. A vending company has ordered 4 of these units, and because all are packaged identically, the selection will be at random. What is the probability that at least 2 units are good?
P(defective) = 3/12 = 1/4 P(good) = 1 - 1/4 = 3/4 [tex]P(2\ good)=4C2\times0.75^{2}\times0.25^{2}=0.211[/tex] [tex]P(3\ good)=4C3\times0.75^{3}\times0.25=0.422[/tex] [tex]P(4\ good)=0.75^{4}=0.316[/tex] The probability that at least 2 units are good is given by: P(2 good) + P(3 good) + P(4 good) = 0.211 + 0.422 + 0.316 = 0.949.
