# Permutation/Combination Problem Help

• Oct 18th 2008, 08:10 PM
HardyHar
Permutation/Combination Problem Help
Hello, all.

I got the problem

(a) xP2

(b)
xC2

The answers in the back of the book say (a)
X2-X and (b) X2-X over 2

I can do these problems normally, but when they threw the X in there, it confused me greatly. Anyone able to lead me in the right direction?

--Thanks
• Oct 18th 2008, 08:27 PM
Chris L T521
Quote:

Originally Posted by HardyHar
Hello, all.

I got the problem

(a) xP2

(b)
xC2

The answers in the back of the book say (a)
X2-X and (b) X2-X over 2

I can do these problems normally, but when they threw the X in there, it confused me greatly. Anyone able to lead me in the right direction?

--Thanks

The x shouldn't be much of an issue...

$_x P_2=\frac{x!}{(x-2)!}=\dots$

$_x C_2=\frac{x!}{2!(x-2)!}=\dots$

Just note that $x!=x(x-1)(x-2)!$

Can you take it from here??

--Chris
• Oct 18th 2008, 08:32 PM
HardyHar
Quote:

Originally Posted by Chris L T521
The x shouldn't be much of an issue...

$_x P_2=\frac{x!}{(x-2)!}=\dots$

$_x C_2=\frac{x!}{2!(x-2)!}=\dots$

Just note that $x!=x(x-1)(x-2)!$

Can you take it from here??

--Chris

Yes, sir. Thank you.