Introduction Permutation and Combination is an important concept in statistics. The reason is because in order to know the probability of an event. we often have to calculate sample space.
Two words are essential regard to permutation and combination, one is order another is replacement. One quick example will be the combination (general meaning) of letters AB. If order matters AB and BA are different, we count them as 2, but if order does not matter, we only count as 1.