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    In a class of 20 pupils, 7 are left handed, and 13 right handed. 5 pupils are selected at random from the class; the order in which they are chosen is not important.

    i) find no. of possible selections in which 2 of the 5 are LH and 3 are RH.
    I got this to be 7C2 x 13C3 which = 6006.

    ii)find the probability that the sample of 5 will include 2 or fewer who are left handed??
    (The answer is supposed to be 0.793 but im not sure how to get that???)

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    One way is to find the no. of selections with zero left handed, then the no. with 1 left-handed and the no. with 2 left-handed (done, 6006). Add together, then divide by the no. of ways of selecting any 5 pupils.
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    Wow. got the right answer 1st time
    thank you
 
 
 
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Updated: April 3, 2011

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