Question

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.

Answer 1

Number of good pens = 132 

Number of defective pens = 12 

Total number of pens = 132 + 12 = 144 

∴ Total number of outcomes in taking a pen at random = 144. 

No. of favourable outcomes in taking a good pen = 132. 

∴ Probability of taking a good pen

= \(\frac{No.\,of\,favourable\,outcomes}{Total\,no.\,of\,outcomes}\)

= \(\frac{132}{144}=\frac{11}{12}\)