从2n只鞋中取4只,有C(2n,4)种取法；从n双鞋中k双,有C(n,k)种方法；从余下的n-k双中取出4-2k双,然后从中各取一只,有C(n-k,4-2k)*2^(4-2k)种方法；于是P(恰好有K双配对)=C(n,k)*C(n-k,4-2k)*2^(4-2k) / C(2n,4) （K=0,...