Remember that combinations are a way to calculate the total outcomes of an event where order of the outcomes does not matter. To calculate combinations, we will use the formula nCr = n! / r! * (n - r)!, where n represents the number of items, and r represents the number of items being chosen at a time.

What is the rule for combination?

The number of combinations of n objects taken r at a time is determined by the following formula: C(n,r)=n! (n−r)!

Why do we multiply to find combinations?

Whenever we have a situation in which two events can happen simultaneously, we simply “multiply” all the cases. 1- Please remember that whenever we come across a situation involving 2 or more events and each event can happen simultaneously, i.e., event 1, event 2, event 3 and so on, all can happen simultaneously.