1. ## Permutation and Combination

Can someone explain the basic difference between permutation and combination?

Are there a formula(s) to know?

2. Originally Posted by magentarita
Can someone explain the basic difference between permutation and combination?
Permutations are order driven: the number of ways to form a queue.
Combinations are content driven: the number of ways to form a collection.

Originally Posted by magentarita
Are there a formula(s) to know?
$\displaystyle P\left( {N,k} \right) = \frac{{N!}}{{\left( {N - k} \right)!}} = N(N - 1)(N - 2) \cdots (N - k + 1)$

$\displaystyle C(N,k) = {{N} \choose {k}}= \frac{{N!}}{{k!\left( {N - k} \right)!}}$

3. ## great notes

Originally Posted by Plato
Permutations are order driven: the number of ways to form a queue.
Combinations are content driven: the number of ways to form a collection.

$\displaystyle P\left( {N,k} \right) = \frac{{N!}}{{\left( {N - k} \right)!}} = N(N - 1)(N - 2) \cdots (N - k + 1)$

$\displaystyle C(N,k) = {{N} \choose {k}}= \frac{{N!}}{{k!\left( {N - k} \right)!}}$
Thank you for the great formulas and definitions.