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

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Numbers of pens

= Numbers of defective pens + Numbers of good pens

∴ Total number of pens = 132 + 12 = 144 pens

P(E) = (Number of favourable outcomes/ Total number of outcomes)

P(picking a good pen)

= 132/144

= 11/12

= 0.916

Answer 2

Answer:

Total no.of pens n(s)=144(12+132)

Out of 144 pens 12 are defective and 132 are non defective(good one)

Out of 144 pens 132 are good one

Let 'E' be the favourable outcome of getting good pens out n(E) =132

Probability P(E) =n(E) /n(s)

➡️P(E) =132/144

➡P(E)=66/72

️➡️P(E)=33/36

➡️P(E)=11/12

➡️P(E)=0.91666