Question

What does $n$and $r$ stands for in combinations?

Answer 1

Combination:

A combination is the selection of elements from a given set where the order does not matter.

The $n$in the term ${}^n{C}_r$ denotes the total number of elements in a set.

The $r$in the term ${}^{n}C_r$denotes the number of elements to be selected and arranged from the total number of elements.

${}^{n}C_r=\frac{n!}{r!\left(n-r\right)!}$ where $n$is the total number of elements and $r$is the elements to be selected and arranged.

The selection neither considers the order of selection nor the repetition of elements