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Math Help - challenging probability problem

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    challenging probability problem

    A drawer has red socks and black socks. You take two socks out at random and the probability that both are red is exactly 1/2. How many socks are in the drawer?
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  2. #2
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    Quote Originally Posted by acc100jt View Post
    A drawer has red socks and black socks. You take two socks out at random and the probability that both are red is exactly 1/2. How many socks are in the drawer?
    Well this probability is:

    <br />
P(r,r)=\frac{n_r}{N}\times \frac{n_r-1}{N-1} = 1/2<br />

    Trial and error shows that n_r=3,\ N=4 is a solution, but is
    it the only solution?

    RonL
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