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# In a pack of a dozen pens, three pens are defective. If a customer buy

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Math Expert
Joined: 02 Sep 2009
Posts: 52902
In a pack of a dozen pens, three pens are defective. If a customer buy  [#permalink]

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02 Oct 2018, 01:37
00:00

Difficulty:

5% (low)

Question Stats:

94% (01:34) correct 6% (03:10) wrong based on 36 sessions

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In a pack of a dozen pens, three pens are defective. If a customer buys two pens, selected at random from the pack, what is the probability that he has no defective pen?

(A) 1/7
(B) 2/11
(C) 6/11
(D) 7/11
(E) 8/11

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Intern
Joined: 21 Nov 2016
Posts: 37
Re: In a pack of a dozen pens, three pens are defective. If a customer buy  [#permalink]

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02 Oct 2018, 02:32
1
We have a dozen pens. That is we have 12 pens. Out of which 3 are defective. That is the good pens remaining are 9.
So Total pens = 12
Defective pens = 3
Good pens = 9
We need to select 2 pens out of the total pens and know their probability of them being good.
So, first pen = no. of good pens/ total pens = 9/12
Second pen = no. of remaining good pens/ no. of remaining total pens = 8/11
total probability = (9/12)x(8/11) = 6/11
So, the correct answer is C.
Re: In a pack of a dozen pens, three pens are defective. If a customer buy   [#permalink] 02 Oct 2018, 02:32
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