1. ## Matrices and permutations

I've been going over some review for some placement test I have to take, I've never done anything with Matrices (I think that's the plural for Matrix, haha) and I'm ruuuuusty on solving permutations:

I don't think these are particularly difficult, I'm just slow in the subjects..Thanks for anyone who can clarify

2. Originally Posted by doomgaze
I've been going over some review for some placement test I have to take, I've never done anything with Matrices (I think that's the plural for Matrix, haha) and I'm ruuuuusty on solving permutations:

I don't think these are particularly difficult, I'm just slow in the subjects..Thanks for anyone who can clarify
$|A|$ means the determinant of a matrix. For a 2x2 matrix, that is a matrix with 2 rows and 2 columns:
$\left[\begin{array}{cc}a&b\\c&d\end{array}\right]$

the determinant is $|A| = ad-bc$.

And if the determinant is zero, the matrix does not have an inverse.

3. (34) if you are considering the ways in which the committee of 3 people is chosen without order

$7C3 = \frac{7!}{3!(7-3)!} = \frac{7!}{3! \times 4!}$

4. Originally Posted by harish21
(34) if you are considering the ways in which the committee of 3 people is chosen without order

$7C3 = \frac{7!}{3!(7-3)!} = \frac{7!}{3! \times 4!}$
so you take the total amount of people then divide (total - the # of people per group) ?

5. Originally Posted by doomgaze
so you take the total amount of people then divide (total - the # of people per group) ?
We are NOT taking the total amount/number of people here. The exclamation mark ! that you see after the numbers is called factorial.

7!= 1*2*3....*7
3!= 1*2*3
4!= 1*2*3*4

To know how this formula comes, you need to study permutations and combinations..Google it.

6. Originally Posted by harish21
We are NOT taking the total amount/number of people here. The exclamation mark ! that you see after the numbers is called factorial.

7!= 1*2*3....*7
3!= 1*2*3
4!= 1*2*3*4

To know how this formula comes, you need to study permutations and combinations..Google it.

Yeah I knew they were factorials, I guess I just didn't express it when I was trying to explain what I thought you said.

Thanks for the link, it is clearing things up.