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# M17 #17

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Manager
Joined: 25 Jul 2010
Posts: 141

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09 Oct 2010, 01:51
If a bin contains twenty cards numbered 1, 2, ..., 20, what is the probability that the sum of the numbers on two cards extracted from the bin will be even?
A) 1/3
B) 7/18
C) 4/9
D) 9/19
E) 1/2
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Joined: 02 Sep 2010
Posts: 803
Location: London

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09 Oct 2010, 01:54
Orange08 wrote:
If a bin contains twenty cards numbered 1, 2, ..., 20, what is the probability that the sum of the numbers on two cards extracted from the bin will be even?
A) 1/3
B) 7/18
C) 4/9
D) 9/19
E) 1/2

Total ways to choose two cards = 20x19

Ways to choose two cards with even sum = Ways to choose two odd cards + Ways to choose two even cards = 10*9 + 10*9

Probability = (10*9 + 10*9)/(20*19) = 9/19

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Re: M17 #17   [#permalink] 09 Oct 2010, 01:54
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# M17 #17

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