Month: June 2020

Dr. J’s Guide to Combinations (without replacement)

Dr. J introduces combinations (without replacement) which is an unordered set of k elements taken from a set of n elements where elements cannot be repeated. He provides intuition behind the formula for combinations, which is n factorial divided by (n-k) factorial times k factorial. Namely, combinations (without replacement) are just permutations (without replacement) except …

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Dr. J’s Guide to Counting

Dr. J introduces the four basic types of counting: combinations and permutations both with and without replacement. Combinations occur when order does not matter while permutations occur when order does matter. The video shows examples of using formulas to perform the counting for each the four basic types of counting.