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Macedon
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Ps: combination Updated on: 12 Jul 2008, 14:06
Originally posted by Macedon on 09 Oct 2005, 02:26.
Last edited by Macedon on 12 Jul 2008, 14:06, edited 1 time in total.
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maxn
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Ps: combination 09 Oct 2005, 05:18
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Not easy wording. I would first calculate what is the probability that the buyer has both items:

- The probability that the first item picked from the 10 is already choosen by the buyer is 3/10

- The probability that the second random picked item is already choosen by the buyer is 2/9

- The probability that both of the random items have been choosen by the buyer is 3/10* 2/9 = 1/15

Then, the probability that the buyer does not have both random picked items is 1 - 1/15 = 14/15
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ywilfred
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I haven't got a clue what this question is about? What does the last line mean?
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qpoo
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Ps: combination 09 Oct 2005, 10:18
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the buyer can choose 1 item out of 10, then choose 2 randomly out of the remaining 9. The possibility that he choose both of them as desired is:
2/9 * 1/8 = 1/36

The possibility of not being able to do so is: 35/36
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nakib77
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I got 3/10 in first attempt and 2/9 in second attempt.
so probability of getting 2 is 3/10*2/9 = 1/15

so probablity of not getting 2 is 1-1/15 =14/15.
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ywilfred
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vikramm
qpoo
the buyer can choose 1 item out of 10, then choose 2 randomly out of the remaining 9. The possibility that he choose both of them as desired is:
2/9 * 1/8 = 1/36

The possibility of not being able to do so is: 35/36

How did you get 1/8 ??
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1/8 is for the third pick. Last pick has only 8 items and 1 favorable outcome.

(PS: I still feel the wording is very hard to follow and the GMAT wouldn't make a question like this. To be frank, this is the first time I have seen a question worded this way)
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maxn
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Still not so sure about the asnwer. There is a bit of a paradox here, not so clear...

If the buyer already selected item 1 out of the 10, how can he select it again? Especially because once you pick item 2, you pull it out from the pot, assuming correctly that there are no duplicates, so why there should be another duplicate of item 1?

Am I wrong? Am I over-thinking here?

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sudhagar
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I couldn't get the conflict part in the question. Is this a valid one? Do we have an OA and explanation?



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