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

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SUMMARY

The problem involves arranging 9 books with specific color groupings: 4 red, 3 green, and 2 gray. The correct method to calculate the arrangements, ensuring that books of the same color are grouped together, is to use the formula (4! * 3! * 2!) * 3!. This accounts for the internal arrangements of the books within each color group and the arrangement of the color groups themselves. The initial misunderstanding stemmed from interpreting the question as requiring only the arrangement of color groups without considering the individual books.

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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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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:
 
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...".
 

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