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

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

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04 Nov 2008, 13:29
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

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?

1
2
5
6
7
Senior Manager
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04 Nov 2008, 13:59
I would guess 2 on this

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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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05 Nov 2008, 03:09
Choice B is correct and so is the explanation. The source is kaplan.
Re: probability ..confusing   [#permalink] 05 Nov 2008, 03:09
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