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# 4 A shipment of 8 television sets contains 2 black-and-white

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4 A shipment of 8 television sets contains 2 black-and-white [#permalink]  14 May 2008, 11:36
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4
A shipment of 8 television sets contains 2 black-and-white sets and 6color sets. If 2
television sets are to be chosen at random from this shipment, what is the probability
that at least 1 of the 2 sets chosen will be a black-and-white set?
A. 1/7 B. ¼ C. 5/14 D. 11/28 E. 13/26

Current Student
Joined: 31 Aug 2007
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Re: PS-Tvs [#permalink]  14 May 2008, 11:49
i'm getting 13/28 but that's not a choice...
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Re: PS-Tvs [#permalink]  14 May 2008, 12:00
young_gun wrote:
i'm getting 13/28 but that's not a choice...

I am also getting 13/28

1-6c2/8c2
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Re: PS-Tvs [#permalink]  14 May 2008, 12:09
young_gun wrote:
i'm getting 13/28 but that's not a choice...

1 - (6/8)(5/7)

VP
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Re: PS-Tvs [#permalink]  14 May 2008, 12:35
kidderek wrote:
young_gun wrote:
i'm getting 13/28 but that's not a choice...

1 - (6/8)(5/7)

Yep Iam getting 13/28 with the same approach. But the OA given for this problem is E.The problem is from Set 25
Manager
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Re: PS-Tvs [#permalink]  14 May 2008, 19:05
rpmodi wrote:
young_gun wrote:
i'm getting 13/28 but that's not a choice...

I am also getting 13/28

1-6c2/8c2

can you explain how you got 6c2 and 8c2? combination is one of my weak areas...
Senior Manager
Joined: 19 Apr 2008
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Re: PS-Tvs [#permalink]  14 May 2008, 22:24
seongbae wrote:
rpmodi wrote:
young_gun wrote:
i'm getting 13/28 but that's not a choice...

I am also getting 13/28

1-6c2/8c2

can you explain how you got 6c2 and 8c2? combination is one of my weak areas...

seongbae ,

Here total number of choice for TV set is 8 (2 b&w ; 6 color ) , by combination logic if we have to select two TV set out of 8 , it is

8c2= 8!/(2!(8-2))!

Now if we have to find the pobability that atleast 1 TV is B&W , easier method is to find the probability of no B&W TV chosen which means 2 TV sets are chosen from 6 color TV ; by the same logic explained above , number of way we can select 2 TV out of 6 will be 6c2. And so probability of chosing 2 TV set from 6 color TV set will be 6c2/8c2 .

To get aleast one B&W TV , we simply subtract 6c2/8c2 from 1 .
Re: PS-Tvs   [#permalink] 14 May 2008, 22:24
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