The combination is explained as selecting r series which can be finished out of all n events. It is signified by nCr that sequentially is equivalent to n!/r!(n-r)!
Combinations are said to be as the littered sequence of numbers of set elements. For instance, given the set of alphabets {a,b,c}{a,b,c}, the combinations of size 2 (take 2 essentials from the group) are {a,b}{a,b}, {a,c}{a,c}, as well as {b,c}{b,c}. It is important to know that the sequence of the series is not a matter here as {b,a}{b,a} is deliberated similar as {a,b}{a,b}.

Rules

We use combinations if an issue arise for the number of tricks of choosing things along with the series of choice is not to be considered.

The values of the given combinations of n factors, reserved r at a time is:
nCr = n!/(r!)(n-r!)= n (n-1)(n-2)…to r factors / r!

While solving combinations, when n = r, the value of combinations is constantly equal to 1.