# Permutations HELP!

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• Nov 21st 2008, 08:51 AM
cnmath16
Permutations HELP!
Hi, I am currently learning Grade 12 Data Management online and I have come across a few questions that I am stuck on.

They are:

Solve for n where:

a) n! divided by (n - 2)! = 930 (4 marks)

b) P(n,5) = 42 x P (n, 3) (5 marks)

21. a) From the word parallel ...
a) How many arrangements can be formed from all the letters in the word parallel?
My answer:
8! divided by 3! 2! = 3360 (because there are 8 letters total, divided by 3 of the same letter 'L' and 2 of the same letter 'A')

b) In how many of these arrangements will the 3 "l's" be together?

If someone could help me that would be greatly appreciated!!
• Nov 21st 2008, 09:08 AM
Plato
Quote:

Originally Posted by cnmath16
Solve for n where:
a) n! divided by (n - 2)! = 930 (4 marks)
b) P(n,5) = 42 x P (n, 3) (5 marks)
21. a) From the word parallel ...
a) How many arrangements can be formed from all the letters in the word parallel?
My answer:
8! divided by 3! 2! = 3360 (because there are 8 letters total, divided by 3 of the same letter 'L' and 2 of the same letter 'A') CORRECT

b) In how many of these arrangements will the 3 "l's" be together?

$\frac {n!}{(n-2)!}=n(n-1)$

$P(n,k)=\frac{n!}{(n-k)!}$

21.b. $\frac{6!}{2!}$. WHY?