12 defective pens are accidentally mixed up the 132 good ones. It is not possible to just look at a pen and tell whether it is defective or not. One pen is taken out at random from the lot. Find the probability that the pen taken out is ]
(i) a good one,
(ii) defective
Number of defective pens in the lot = 12
Number of good pens in the lot = 132
Total number of pens in the lot = 12 + 132 = 144
∴ Total number of outcomes = 144
(i) There are 132 good pens in the lot. Out of these pens, one good pen can be taken out in 132 ways.
Favourable number of outcomes = 132
$\therefore P(P e n$ taken out is good one $)=\frac{\text { Favourable number of outcomes }}{\text { Total number of outcomes }}=\frac{132}{144}=\frac{11}{12}$
(ii) There are 12 defective pens in the lot. Out of these pens, one defective pen can be taken out in 12 ways.
Favourable number of outcomes = 12
$\therefore P(P$ en taken out is defective $)=\frac{\text { Favourable number of outcomes }}{\text { Total number of outcomes }}=\frac{12}{144}=\frac{1}{12}$
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