combination

In mathematics, combinations refer to the selection of items from a set where the order of selection does not matter. This is distinct from permutations, where the order of selection is significant.1

For example, if you have five letters (A, B, C, D, E) and you want to select two, a permutation would consider AB and BA as different outcomes. However, in a combination, AB and BA are considered the same selection. The number of combinations can be calculated using the formula:

[
_nC_k = \frac{n!}{k!(n-k)!}
]

where n is the total number of items available, and k is the number of items to choose. Combinations are a fundamental concept in probability theory and are used to count the number of possible outcomes in various scenarios.12