Dr. J’s Guide to Permutations with Replacement

Dr. J introduces delves into more detail on permutations with replacement including intuition behind the formula and additional examples. To aid the intuition, the Fundamental Rule of Counting is introduced that states “if there are a ways of doing one thing and b ways of doing another thing, then there are a times b ways of doing those two things together.” This is used to “derive” the formula for permutation with replacement (n^k where k is the number of elements in the resulting set and n is the number of elements in the original set). This formula is used to assess the number of possible passwords available in different password policies.