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# gmat club m05 Q17

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Joined: 15 Feb 2010
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02 Apr 2010, 15:35
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Difficulty:

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Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 2 sessions

Kate and David each have $10. Together they flip a coin 5 times. Every time the coin lands on heads, Kate gives David$1. Every time the coin lands on tails, David gives Kate $1. After the coin is flipped 5 times, what is the probability that Kate has more than$10 but less than $15? A. 5/16 B. 15/32 C. 1/2 D 21/32 E 11/16 i can't understand their explanation please help! Manager Joined: 20 Mar 2010 Posts: 84 Followers: 2 Kudos [?]: 95 [1] , given: 1 Re: gmat club m05 Q17 [#permalink] ### Show Tags 02 Apr 2010, 22:41 1 This post received KUDOS If Kate has to win more than$10 but less than $15 she has to win at least 3 times and at most 4 times. If she wins 1 or 2 times she will have less than$10 at the end whereas if she wins all the 5 times shell will have $15 The probability that Kate has more than$10 but less than \$15
= probability of getting 3 tails in 5 tosses + probability of getting 4 tails in 5 tosses
= 5c3 * (1/2)^3* (1/2)^2 + 5c4 *(1/2)^4 * (1/2)
=15/32

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Re: gmat club m05 Q17   [#permalink] 02 Apr 2010, 22:41
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