Question

24 defective pens are accidentally mixed with 120 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 is taken out is a good one.

A 0.865 Correct Answer Incorrect Answer
B 0.870 Correct Answer Incorrect Answer
C 0.833 Correct Answer Incorrect Answer
D 0.858 Correct Answer Incorrect Answer
E None of these Correct Answer Incorrect Answer

Solution

Numbers of pens = Numbers of defective pens + Numbers of good pens
∴ Total number of pens = 120 + 24 = 144 pens
P(E) = (Number of favourable outcomes) / (Total number of outcomes)
P(picking a good pen) = 120/144 = 0.833

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