My Math Forum Permutation or combination??

 Abstract Algebra Abstract Algebra Math Forum

 April 11th, 2008, 06:46 AM #1 Newbie   Joined: Apr 2008 Posts: 1 Thanks: 0 Permutation or combination?? Hello every one I am a new member and I am happy to join this good forum actually I need your help I have the following problem and I am confused so can you please help me solving it Find the value of x in the following: (a) x = 3nC35 – n + n + 18C3n (b) 10 × x + 3Cx – 2 = x + 3P3
 April 11th, 2008, 09:59 AM #2 Global Moderator     Joined: Nov 2006 From: UTC -5 Posts: 16,046 Thanks: 938 Math Focus: Number theory, computational mathematics, combinatorics, FOM, symbolic logic, TCS, algorithms What's confusing? How far can you get?
 June 5th, 2008, 02:29 PM #3 Senior Member   Joined: May 2008 From: Sacramento, California Posts: 299 Thanks: 0 The first one already gives you what x is. I think you might be having trouble because you might be thinking "I need a single number, not a whole expression". But keep in mind you have 4 variables. The first one can be simplified by first multiplying all the numbers of a single term, canceling n's out, and adding together like this: [color=darkred]a) x= 105Cn + 54Cn x= 159Cn That's about as far as it can be simplified.[/color] [color=darkblue]b) 10x + 3Cx – 2= x + 9P (9P=3P3) To isolate x here, you can substract 9P 10x + 3Cx - 2 - 9P= x You can factor this. x= x(10 + 3C) - (2 + 9P) You now substract x(10 + 3C), unfactor, and substract like terms. -9x - 3Cx= -(2 + 9P) Refactor (again!). I am doing all this factoring and unfactoring to make you see how you can multiply and divide. -x(9 + 3C)= -(2 + 9P) Divide each side by -(9+3C). x= -(2 + 9C)/-(9 + 3C) x= (2 + 9C)/(9 + 3C) x= (2 + 9C)/3(3+C)[/color] Those would be your values. Can anyone check my answer for me?

### permutation math 3c

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