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# There are 6 cards numbered from 1 to 6. They are placed into

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There are 6 cards numbered from 1 to 6. They are placed into [#permalink]  09 Sep 2008, 04:46
There are 6 cards numbered from 1 to 6. They are placed into a box, and then one is drawn and put back and then another card is drawn and put back. What is the probability that one of the cards was 5 if the sum of the two was 8?

1
2/3
1/2
2/5
1/5
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Re: card probability [#permalink]  09 Sep 2008, 04:56

The first card could be a 5 or 3. The second card needs to be either 3 or 5 respectively.

Thus, probability of first card being 5 and second card being 3 = 1/6 + 1/6 = 1/3
Similarly, probability of first card being 3 and second card being 5 = 1/6 + 1/6 = 1/3

Combining both, it should be 1/3 + 1/3 = 2/3.

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Re: card probability [#permalink]  09 Sep 2008, 05:40
arjtryarjtry wrote:
There are 6 cards numbered from 1 to 6. They are placed into a box, and then one is drawn and put back and then another card is drawn and put back. What is the probability that one of the cards was 5 if the sum of the two was 8?

1
2/3
1/2
2/5
1/5

possible combinations:
3,5
5,3
2,6
6,2
4,4

probability= 2/5
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Current Student
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Posts: 562
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Re: card probability [#permalink]  09 Sep 2008, 07:15
i thought the ans should be 1/6*1/6 + 1/6*1/6.

there are totally 6 ways of picking up the cards right?
thats what is the definiton of possible cases. its possible to pick up any of the 6 cards right?
SVP
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Posts: 1828
Location: New York
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Kudos [?]: 551 [0], given: 5

Re: card probability [#permalink]  09 Sep 2008, 07:31
arjtryarjtry wrote:
i thought the ans should be 1/6*1/6 + 1/6*1/6.

there are totally 6 ways of picking up the cards right?
thats what is the definiton of possible cases. its possible to pick up any of the 6 cards right?

Read the question again.. and ...again
What is the probability that one of the cards was 5 if the sum of the two was 8?
_________________

Smiling wins more friends than frowning

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Joined: 17 Jun 2008
Posts: 1570
Followers: 12

Kudos [?]: 202 [0], given: 0

Re: card probability [#permalink]  09 Sep 2008, 09:24
x2suresh wrote:
arjtryarjtry wrote:
There are 6 cards numbered from 1 to 6. They are placed into a box, and then one is drawn and put back and then another card is drawn and put back. What is the probability that one of the cards was 5 if the sum of the two was 8?

1
2/3
1/2
2/5
1/5

possible combinations:
3,5
5,3
2,6
6,2
4,4

probability= 2/5

Thanks x2suresh. I wish I could think probability problems in these simple terms....not sure why I have got fobia to probability.
Current Student
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Re: card probability [#permalink]  09 Sep 2008, 09:26
x2suresh wrote:
arjtryarjtry wrote:
i thought the ans should be 1/6*1/6 + 1/6*1/6.

there are totally 6 ways of picking up the cards right?
thats what is the definiton of possible cases. its possible to pick up any of the 6 cards right?

Read the question again.. and ...again
What is the probability that one of the cards was 5 if the sum of the two was 8?

hmm..
i still think that the problem is not well worded...
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Joined: 03 Jun 2008
Posts: 136
Schools: ISB, Tuck, Michigan (Ross), Darden, MBS
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Re: card probability [#permalink]  09 Sep 2008, 10:43
arjtryarjtry wrote:
x2suresh wrote:
arjtryarjtry wrote:
i thought the ans should be 1/6*1/6 + 1/6*1/6.

there are totally 6 ways of picking up the cards right?
thats what is the definiton of possible cases. its possible to pick up any of the 6 cards right?

Read the question again.. and ...again
What is the probability that one of the cards was 5 if the sum of the two was 8?

hmm..
i still think that the problem is not well worded...

I found no ambiguity in the question.

ans is clearly 2/5
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Re: card probability   [#permalink] 09 Sep 2008, 10:43
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