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A lot consists of 144 ball pens of which 20 are defective and others good. Nun 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?

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No. of good pens = 144 – 20 = 24

No. of detective pens = 20

Total no. of possible outcomes = 144 {total no pens}

(i) E ⟶ event of buying pen which is good.

No. of favourable outcomes = 124 {124 good pens}

P(E) = (No.of favorable outcomes)/(Total no.of possible outcomes)

P(E) = 124/144 = 31/36

(ii) Bar  E⟶ event of not buying a pen which is bad P(E) + P(Bar E) = 1

P(E)+P(Bar E)=1

P(Bar E) = 1 - P(E)

=1−31/36 = 5/36

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