Q1 of 19 Page 302

15 defective ballpens are accidentally mixed with 135 good ones. It is not possible to just look at a ballpen and say whether it is defective or not. One ballpen is picked up at random from it. Find the probability that the ballpen selected is a good one.

Given, Total number of defective ballpens = 15


and total number of good ballpens = 135


Therefore, total number of ball pens = number of defective ballpens + number of good ball pens


So, total number of ball pens = 15 + 135 = 150


Now, let E be the event that the ballpen picked is defective and F be the event that the ballpen picked is good.


Therefore, the number of favourable outcomes of event E = 15


and , the number of favourable outcomes of event F = 135


Total number of favourable outcomes = 15 + 135 = 150


Probability that the ball pen selected is good = Probability of event F occuring = P(F)


P(F) = = = 0.9


So, the probability that the ballpen selected is good is 0.9.


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