Permutation
- leonardo shawon
- Posts:169
- Joined:Sat Jan 01, 2011 4:59 pm
- Location:Dhaka
in how many ways N-numbered letters can be arranged where TWO special letters will not be located in first or last of a row...
Ibtehaz Shawon
BRAC University.
long way to go .....
BRAC University.
long way to go .....
Re: Permutation
Fill up the first and the last place at first.
$(n-2) \cdot (n-2) \cdot (n-3) \cdots 2 \cdot 1 \cdot (n-3)=(n-2)(n-3)\cdot (n-3)!$
Edit: Corrected!
$(n-2) \cdot (n-2) \cdot (n-3) \cdots 2 \cdot 1 \cdot (n-3)=(n-2)(n-3)\cdot (n-3)!$
Edit: Corrected!
"Inspiration is needed in geometry, just as much as in poetry." -- Aleksandr Pushkin
Please install LaTeX fonts in your PC for better looking equations,
learn how to write equations, and don't forget to read Forum Guide and Rules.
Please install LaTeX fonts in your PC for better looking equations,
learn how to write equations, and don't forget to read Forum Guide and Rules.
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- Posts:135
- Joined:Thu Dec 09, 2010 12:10 pm
Re: PERMUTATION
আমি পোস্ট লিখে সাবমিট করে দেখি মুন ভাইয়া দিয়া দিল... যাউকগা আমারটাও দিলাম...
moon vaia, wouldn't it be $\left( n-2\right) \left( n-3 \right) \left( n-2 \right)!$ ? as repetition isn't allowed...
moon vaia, wouldn't it be $\left( n-2\right) \left( n-3 \right) \left( n-2 \right)!$ ? as repetition isn't allowed...
Re: Permutation
Yup...you are right. Actually at first I thought that repetition is allowed...later I edited it, and edited incorrectly.
"Inspiration is needed in geometry, just as much as in poetry." -- Aleksandr Pushkin
Please install LaTeX fonts in your PC for better looking equations,
learn how to write equations, and don't forget to read Forum Guide and Rules.
Please install LaTeX fonts in your PC for better looking equations,
learn how to write equations, and don't forget to read Forum Guide and Rules.
- leonardo shawon
- Posts:169
- Joined:Sat Jan 01, 2011 4:59 pm
- Location:Dhaka
Re: Permutation
moon bhaia,, can u please elaborate? Im not good!
Ibtehaz Shawon
BRAC University.
long way to go .....
BRAC University.
long way to go .....
-
- Posts:135
- Joined:Thu Dec 09, 2010 12:10 pm
Re: Permutation
first fill up the first place, you can do this in $(n-2)$ ways(you can't consider those 2 special letters), then you can fill up last place in $(n-3)$ ways(as repetition isn't allowed, you have put a letter in first place already)... then $(n-2)$ letters can be arranged in $(n-2)!$ ways...
ok?
ok?
- leonardo shawon
- Posts:169
- Joined:Sat Jan 01, 2011 4:59 pm
- Location:Dhaka