should be (20 choose 4) = (20)(19)(18)(17)/24
第二题答案是不是:C(16+3,3)+C(15+3,3)+...+C(1+3,3)+C(0+3,3)
I think we should change 16 to 20....we get C(24,4)=...
how to understand: must be invested among 4 possible opportuniti
even if we should change 16 to 20....we get C(21,4)=...
sorry, C(21,4)=... wrong; C(24,4)=... right,if we should change
you are right:C(20,4)=C(16+3,3)+C(15+3,3)+...+C(1+3,3)+C(0+3,3)
第二题:What if not all money need be invested? 可这样理解：
皆兄弟也
2010-09-08 09:10:55第二题答案是不是:C(16+3,3)+C(15+3,3)+...+C(1+3,3)+C(0+3,3)