Permutations: Arranging Red, Green & Gray Books on a Shelf

  • Thread starter Government$
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In summary, if books of the same color must be arranged together, there are 4!3!2!3! ways to arrange 9 books with 4 red, 3 green, and 2 gray covers on a shelf. This includes the stipulation that books of the same color must be arranged together.
  • #1
Government$
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Homework Statement



1.) 4 of the books have red covers, 3 have green covers, and another 2 have gray covers. In how many ways can the books be arranged on a shelf if books of the same color must be arranged together?


The Attempt at a Solution



1) I think that the answer here is 3!

But here is the answer from my book (4!3!2!)3!
 
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  • #2
Hi Government$! :smile:
Government$ said:
1.) 4 of the books have red covers, 3 have green covers, and another 2 have gray covers. In how many ways can the books be arranged on a shelf if books of the same color must be arranged together?

1) I think that the answer here is 3!

That's correct only if books of the same colour are stuck together! :wink:
 
  • #3
If the answer they are looking for is 4!3!2!3! it would have been less ambiguous to pose the question as "There are 9 different books. 4 of the books have red covers...".
 

Related to Permutations: Arranging Red, Green & Gray Books on a Shelf

1. How many ways can the red, green, and gray books be arranged on a shelf?

The number of ways the books can be arranged on a shelf is equal to the number of permutations of the three colors. This can be calculated using the formula n! / (n-r)! where n is the total number of colors (3) and r is the number of books being arranged (3). In this case, there are 3! / (3-3)! = 3! = 6 ways to arrange the books.

2. Can the books be arranged in any order or are there restrictions?

As long as all three colors are present and each color has at least one book, the books can be arranged in any order. However, if there were multiple books of the same color, the order of those books would matter in the arrangement.

3. What is the difference between a permutation and a combination?

A permutation is an arrangement where the order of the elements matters, while a combination is a selection of elements where the order does not matter. In this case, arranging the books in a certain order would result in a different permutation, while selecting a group of books without regard to order would result in a combination.

4. How does the number of books being arranged affect the number of permutations?

The number of books being arranged directly affects the number of permutations. As the number of books increases, the number of permutations also increases. This is because there are more ways to arrange a larger number of elements. The formula for calculating permutations takes into account both the total number of elements and the number being arranged.

5. Can the formula for calculating permutations be applied to other scenarios?

Yes, the formula n! / (n-r)! can be applied to any scenario where a specific number of elements are being arranged out of a larger set of elements. For example, arranging a set of letters in a certain order or arranging a group of people in a line. The formula helps to determine the total number of possible arrangements in each scenario.

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