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12 defective pens are accidentally mixed with 132 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 taken out is a good one.

$$\therefore$$ Total number of pens = 132 + 12 = 144 pens
$$P(E) \ = \ \frac{Number \ of \ favourable \ outcomes}{Total \ number \ of \ outcomes}$$
P(picking a good pen) $$= \ \frac{132}{144} \ = \ \frac{11}{12} \ = \ 0.916$$