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In a village there are an equal number of boys and girls of marriageable age. Each boy dates a certain number of girls and each girl dates a certain number of boys. Under what condition is it possible that every boy and girl gets married to one of their dates?(Polygamy and polyandry not allowed)

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Is there a particular reason why you did not accept any of the answers you got on this site? Do you feel that all of them do not answer you question or you just don't know how to accept an answer? More on accepting answers: meta.math.stackexchange.com/questions/3286/… –  Dennis Gulko Mar 13 '13 at 9:05

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What you actually have is a bipartite graph and you are looking for a perfect matching. The theorem that provides a characterization for such conditions is Hall's marriage theorem: There exists a perfect matching for the graph if and only if for any set of boys $B$, $|B|\leq|N(B)|$ where $N(B)$ denotes the set of girls that date at least one of the boys from $B$.

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ya you are right –  kalpeshmpopat Mar 13 '13 at 9:08

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