The prime ministers A,B.C,D,E,F and G of 7 countries wil address at a summit meeting.
a) Find the number of arrangements that can be made so that
i) A will speak before C
ii) A will speak before C and C before E.
b) In how many of those ways in (a) (ii) will C speak immediately after
A?
請附上解釋
f6 math&stat
2009-09-22 3:57 am
回答 (2)
2009-09-22 4:39 am
✔ 最佳答案
ai) A will speak before Cthe number of arrangements = 7! / 2! = 2520(全排列有 7! 個,AC排列 2! 個)
ii) A will speak before C and C before E.
the number of arrangements = 7! / 3! = 840(ACE有 3! 種排列)
b) In how many of those ways in (a) (ii) will C speak immediately after
A?
將 AC 捆在一起當作一個元素 ,共 6 個元素 ,仿a(i)的方法 :
6! / 2! ( AC 及 E 共 2! 種排列) = 360 ways
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