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May 6th, 2015, 07:23 AM  #1 
Newbie Joined: May 2015 From: hong kong Posts: 8 Thanks: 0  Arrangement problems
The prime minister A,B,C,D,E,F and G of 7 countries will 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 ? Thanks!! 
May 6th, 2015, 08:20 AM  #2 
Senior Member Joined: Mar 2011 From: Chicago, IL Posts: 214 Thanks: 77 
(a i) $\displaystyle \binom{7}{2}\cdot 5!$ (a ii) $\displaystyle \binom{7}{3}\cdot 4!$ 
May 6th, 2015, 10:41 AM  #3  
Math Team Joined: Dec 2006 From: Lexington, MA Posts: 3,267 Thanks: 407  Hello, new hand! Quote:
There are possible arrangements. In half of them, A will precede C. Quote:
I'm getting two different answers. I'll have to work on it . . . Quote:
There are: arrangements. In half of them, will precede  
May 8th, 2015, 01:29 PM  #4  
Math Team Joined: Dec 2006 From: Lexington, MA Posts: 3,267 Thanks: 407  Hello, new hand! Quote:
 

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arrangement, combination, permutation, problems 
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