Find the number of different permutations of the letters of the word MASSACHUSETTS.Ħ. In how many ways can 3 English, 3 history, and 2 math books be set on a shelf, if the English books are set on the left, history books in the middle, and math books on the right?ĥ. In how many different ways can five people be seated in a row if two of them insist on sitting next to each other?Ĥ. How many permutations of the letters of the word SECURITY end in a consonant?ģ. How many different ways can this be done?Ģ. A group of 15 people who are members of a volunteer club wish to choose a chair and a secretary. This is also referred to as ordered partitions.ġ. Permutations with Similar Elements: The number of permutations of n elements taken n at a time, with r 1 elements of one kind, r 2 elements of another kind, and so on, such that n = r 1 + r 2 +.Circular Permutations: The number of permutations of n elements in a circle is ( n − 1)!.This gives us the method we are looking for. But we know there are 7! permutations of the letters E 1LE 2ME 3NT. 3! permutations of the letters E 1LE 2ME 3NT.Let us suppose there are n different permutations of the letters ELEMENT. We list them below:īecause the E’s are not different, there is only one arrangement LEMENET and not six. Clearly, there are 3! or 6 such arrangements. Suppose we form new permutations from this arrangement by only moving the E’s. Let us now look at one such permutation, say: Since all the letters are now different, there are 7! different permutations. Suppose we make all of the letters different by labeling the letters as follows. Let us determine the number of distinguishable permutations of the letters ELEMENT. Our next problem is to see how many ways these people can be seated in a circle. We have already determined that they can be seated in a straight line in 3! or 6 ways. Suppose we have three people named A, B, and C. The first problem comes under the category of Circular Permutations, and the second under Permutations with Similar Elements. In how many different ways can the letters of the word MISSISSIPPI be arranged?.In how many different ways can five people be seated in a circle?.In this section we will address the following two problems. Where n and r are natural numbers.Ĭi rcular Permutations and Permutations with Similar Elements Permutations of n Objects Taken r at a Time : n P r = n ( n − 1)( n − 2)( n − 3).Permutations: A permutation of a set of elements is an ordered arrangement where each element is used once.Hence the multiplication axiom applies, and we have the answer (4 P3) (5 P2). For every permutation of three math books placed in the first three slots, there are 5 P2 permutations of history books that can be placed in the last two slots. So the answer can be written as (4 P 3) (5 P 2) = 480.Ĭlearly, this makes sense. Therefore, the number of permutations are 4
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