I may forget the formulae for the 4 scenarios above (ordered with repetition, ordered without repetition, order agnostic with repetition and order agnostic without repetition), but I can figure them out again because they make intuitive sense. I'm starting to learn things intuitively and not by rote, especially mathematical concepts. If you choose two balls with replacement/repetition, there are permutations:, how many combinations are there? Intuitively this number is > (number of combinations without repetition/replacement): Where n is the number of things to choose from, r number of times.įor example, you have a urn with a red, blue and black ball. The number of permutations with repetition (or with replacement) is simply calculated by: There are basically two types of permutations, with repetition (or replacement) and without repetition (without replacement). To open a safe you need the right order of numbers, thus the code is a permutationĪs a matter of fact, a permutation is an ordered combination.A fruit salad is a combination of apples, bananas and grapes, since it's the same fruit salad regardless of the order of fruits.Using the example from my favourite website as of late, : ![]() As you may recall from school, a combination does not take into account the order, whereas a permutation does. While I'm at it, I will examine combinations and permutations in R. Time to get another concept under my belt, combinations and permutations.
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