Question

12 defective ball pens are accidentally mixed with 156 good one. It is not possible to just look at pen and tell whether or not it is defective. The shopkeeper draws one pen at random.

Determine the probability that the pen taken out is a good one.

Suppose the pen drawn is defective. The shopkeeper did not sell out and kept the pen aside. He again draws one more pen at random from the rest. What is the probability that pen is not defective.

Which value is shown by the shopkeeper?
Value Based Question

Answer 1

Probability in case1 =144/168=72/84=36/42=18/21=6/7
Probability in case2=155/168
Value- honest

Answer 2

No.of good pens=156
No.of defective pens=12
Total pens=168

P(E)=no.of favourable outcomes/total no.of outcomes

P(good pen)=156/168

P(good pen)=13/14

Hence probability of good pen is 13/14.
A defective pen is kept aside.
Now,
no.of good pens=156
no.of defective pens=12-1=11
Total no.of pens==167
P(pen is not defective)=no.of good pens/total pens

P(pen is not defective)=156/167

Hence probability of pen not defective is 156/167.


Value shown by the shopkeeper is - whether the pen is good or not.