Answer
A combination is defined as a random arrangement (order is not important) taken all or a few items at a time.
Work Step by Step
We know that a combination of items occurs when the selection is made from the same group and no item is used more than one time (no repetition); also, the order makes no difference.
The formula for a combination is:
${}_{n}{{C}_{r}}=\frac{n!}{r!\left( n-r \right)!}$
For example:
Someone has to select 4 people from a group of 10.
Thus, in this case, a combination is used to determine the number of ways to select 4 people.
