Question
span >19 defective pens are accidentally mixed with 136 good ones. It is not possible to just look at a pen and tell whether or not it is defective. One pen is taken out at random from this lot. Determine the probability that the pen is taken out is a good one.
Solution
Numbers of pens = Numbers of defective pens + Numbers of good pens
∴ Total number of pens = 136 + 19 = 155 pens
P(E) = (Number of favourable outcomes) / (Total number of outcomes)
P(picking a good pen) = 136/155 = 0.877
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