Mathematics
A lot consists of 144 ball pens of which 20 are defective and the others are good. Nuri will buy a pen if it is good, but will not buy if it is defective. The shopkeeper draws one pen at random and gives it to her. What is the probability that
(i) She will buy it ?
(ii) She will not buy it ?
Probability
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Answer
No. of possible outcomes = 144
(i) Nuri will buy pen if it is good.
No. of good pens = 144 - 20 = 124
∴ No. of favourable outcomes = 124
P(drawing a good pen)
= .
Hence, the probability that Nuri will buy the pen = .
(ii) Buying a pen and not buying a pen are complementary events.
∴ P(buying a pen) + P(not buying a pen) = 1
⇒ + P(not buying a pen) = 1
⇒ P(not buying a pen) = 1 -
⇒ P(not buying a pen) = =
Hence, the probability of not buying a pen = .
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