已知全集U={1,2,3,4,5,6,7,8},在U中任取四个元素组成的集合记为A
已知全集U={1,2,3,4,5,6,7,8},在U中任取四个元素组成的集合记为A
A={a1,a2,a3,a4},余下的四个元素组成的集合记为CuA={b1,b2,b3,b4},若a1+a2+a3+a4
U中元素的和为1+2+..+8=8*9/2=36S=a1+a2+a3+a4须小于36/2=18U中任取4个元素的取法有C(8,4)=8*7*6*5/4!=70其中S=18的取法有以下8种:1,2,7,81,3,6,81,4,6,71,4,5,82,3,5,82,3,6,72,4,5,73,4,5,6对于其它70-8=62种取法...