求救！！概率题不会做，jj看不懂

syl88

从小概率没学好啊，都不怎么会做。看到jj里面一题如下：

136书架上１０本书４个软批６个硬皮，问取出５本至少各有１种的有多少情况　　　

２４６种

Sol同129题。C(5.10)-C（5，6）=252-6=246

谁能解释一下怎么做？c(5,10)-c(5,6)是怎么个运算？
谢谢各位啦！！！

lightgarden

Choose 5 from 10, you have C5.10 different combination. The only chance that all 5 belong to the same group is that all 5 are hard cover. The combination of all 5 hard top is C5.6 (choose 5 out from the 6 hard tops). Since there are only 4 soft cover, there is no chance that all 5 books chosen are all soft cover, you don't have to worry about the soft covers.

ykelly123

只有这一种思路吗？。。。乍一看想不到啊。。

syl88

i see... thanks!!!!

wyw1018

只有这一种思路吗？。。。乍一看想不到啊。。

-- by 会员 ykelly123 (2011/9/19 5:57:31)

另外一个思路，稍微麻烦一些：取1本软皮4本硬皮  C(1 4)*C(4 6)
取2本软皮3本硬皮  C(2 4)*C(3 6)
取3本软皮2本硬皮  C(3 4)*C(2 6)
取4本软皮1本硬皮  C(4 4)*C(1 6)
全部相加即可