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几道排列组合,希望牛人帮忙解答,谢谢,从小就没学好.....

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发表于 2012-1-5 00:20:30 | 只看该作者 回帖奖励 |倒序浏览 |阅读模式
Q9:
1. A gardener is going to plant 2 red rosebushes and 2 whiterosebushes.  If the gardener is to selecteach of the bushes at random, one at a time, and plant them in a row, what isthe probability that the 2 rosebushes in the middle of the row will be the redrosebushes?



2. A photographer will arrange 6 people of 6 different heights forphotograph by placing them in two rows of three so that each person in thefirst row is standing in front of someone in the second row.  The heights of the people within each row mustincrease from left to right, and each person in the second row must be tallerthan the person standing in front of him or her.  How many such arrangements of the 6 peopleare possible?

A. 5    B. 6    C. 9   D.24   E.36

Q29:

June 25, 1982, fellon a Friday.  On which day of the weekdid June 25, 1987, fall?  (Note: 1984 wasa leap year.)


Q37:
A jar contains 16 marbles, of which 4 are red, 3 are blue, and therest are yellow.  If 2 marbles are to beselected at random from the jar, one at a time without being replaced, what isthe probability that the first marble selected will be red and the secondmarble selected will be blue?


A.   5

B.   6
C.   9
D.   24
E.   36
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沙发
发表于 2012-7-17 00:44:24 | 只看该作者
第二题的画个图 两排位子 一排三个人 六个人是a<b<C<d<e<f  按题目要求 其实a和f的位子是固定的 第一排第一个和第二排最后一个 然后中间的按要求自己排一下就很快算出来是5种了
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