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Question
4 defective pens are accidentally mixed with 16 good ones. It is not possible to just look at a pen and tell whether or not it is defective. One pen is drawn at random from the lot. What is the probability that the pen is defective?
Solution
Total number of pens = 4 + 16 = 20
Total possible outcomes = 20
Number of defective pens = 4
P(defective pen) = `4/20 = 1/5`
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