Question

I'm feeling a bit rusty with probabiliy. Could somebody quickly explain to me how to use permutations and combinations?
I understand what they mean, but I'm confused at what the xPy or the xCy notation means( where x and y are numbers.

Answer 1

\[ \large xPy = ^xP_y = \frac{x!}{(x-y)!} \]

\[ \large xCy = ^xC_y = \frac{x!}{y! \times (x-y)!} \]

where \( x,y \in \mathbb{N} \)

Answer 2

xPy: It means that there are (x) objects going into (y) categories, order matters

(ie) (x) different cars competing for (y) places in a race: xPy



xCy: It means there are (x) objects going into (y) categories, but order DOES NOT matter:

ie) (x) different cars competing for (y) identical parking spots

Answer 3

Just remember "Permutation" is counting the different ways something can "Permeate" so order matters.

"Combination" is counting different ways to combine the same things so order does not matter.

Answer 4

right ...switched this two