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# Karen has exactly 6 quarters, 5 dimes, and 10 nickels in her

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Manager
Joined: 14 Oct 2008
Posts: 159
Karen has exactly 6 quarters, 5 dimes, and 10 nickels in her [#permalink]

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04 Nov 2008, 13:29
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Karen has exactly 6 quarters, 5 dimes, and 10 nickels in her pocket. If she withdraws a number of these coins at random, how many coins would she have to withdraw to ensure that she has at least a 50 percent chance of withdrawing at least one quarter?

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Senior Manager
Joined: 04 Aug 2008
Posts: 375

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04 Nov 2008, 13:59
I would guess 2 on this

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Joined: 14 Sep 2003
Posts: 45
Location: california

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04 Nov 2008, 17:09
me thinks B as well and here's how

6 quarters, 5 dimes and 10 nickels. If she were to pick 1 coin, the probability of it being a quarter is 6 / 21 ~ .28

Assume the first coin was a dime or a nickel. Now she picks one more coin and the resulting probability for a quarter is 6 / 20 = .3

Since they are discrete events, adding the 2 probabilities, yields 0.28 + 0.3 which is a little more than 50%. Is that the OA?

Gamecode - what is the source of this question? I'm trying to work on some Probability / combinations type problems and would appreciate a pointer to any good source. Thanks!
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04 Nov 2008, 18:53
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The one who flies is worthy. The one who is worthy flies. The one who doesn't fly isn't worthy

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Joined: 14 Oct 2008
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05 Nov 2008, 03:09
Choice B is correct and so is the explanation. The source is kaplan.
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Joined: 09 Sep 2013
Posts: 15913
Re: Karen has exactly 6 quarters, 5 dimes, and 10 nickels in her [#permalink]

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05 Feb 2017, 11:31
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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Re: Karen has exactly 6 quarters, 5 dimes, and 10 nickels in her   [#permalink] 05 Feb 2017, 11:31
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