# Math Help - Permutation.......

1. ## Permutation.......

Hi all, need some help here,

Simplify

2n+2
. .Pn
2n
. .Pn

thanks

2. Originally Posted by micmac63
Hi all, need some help here,

Simplify

2n+2
. .Pn
2n
. .Pn

thanks
Simplify $\frac{^{2n+2}P_n}{^{2n}P_n}$.

Do you know that $^n P_r = \frac{n!}{(n-r)!}$ ?

3. yes, but dont quite understand ?????

4. Originally Posted by mr fantastic
Simplify $\frac{^{2n+2}P_n}{^{2n}P_n}$.

Do you know that $^n P_r = \frac{n!}{(n-r)!}$ ?
Originally Posted by micmac63
yes, but dont quite understand ?????
$\frac{^{2n+2}P_n}{^{2n}P_n} = \frac{\frac{(2n+2)!}{(2n+2-n)!}}{\frac{(2n)!}{(2n-n)!}} = \frac{\frac{(2n+2)!}{(n+2)!}}{\frac{(2n)!}{n!}} = \frac{(2n+2)!}{(n+2)!} \times \frac{n!}{(2n)!} = .....$

5. Thankyou so much, Im helping my daughter with this, and she is on right track now,

if the equation equals 3.5, find the value of n ?

thanks again.

6. Originally Posted by micmac63
Thankyou so much, Im helping my daughter with this, and she is on right track now,

if the equation equals 3.5, find the value of n ?

thanks again.
Solve $\frac{(2n+2)(2n+1)}{(n+2)(n+1)} = \frac{7}{2} \Rightarrow 2(2n+2)(2n+1)=7(n+2)(n+1) .....$

Expand both sides and re-arrange into the form:

Solve this equation in the usual way, noting the restriction $n \geq 0$.