Yes, I agree. My answer is P(2,5)=20. My thought is that I don't care the three red. I just need to put that 1 yeallow and 1 blue in those 5 slots and the rest belongs to red cars. So it's P(2,5).作者: 自尊宝 时间: 2003-3-21 10:57
p5,2 =20 is ok, you need not concider the other identical three .right?作者: 火龙果 时间: 2003-4-7 21:54
因为同色车无顺序,所以应该先排列red car,然后在其4个间隙中放blue car and yellow car,,但要分为两种情况:
1)yellow car & blue car 不相邻,则有P4,2=12;
2)yellow car & bule car 相邻,则有P2,2×C4,1=8
所以,共有12+8=20作者: mindfree 时间: 2003-4-9 23:02
直接P(2,5), 挑出两辆车有顺序的排在两个位置上,其它三辆则位置固定.
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