Combinatorics: Choosing Books on a Shelf

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SUMMARY

The discussion focuses on combinatorial mathematics, specifically calculating the number of ways to arrange three books from a selection of nine English, seven French, and five German books while excluding one language. The solution involves breaking the problem into six distinct cases based on the combinations of languages present. The total number of arrangements calculated is 2412, derived from permutations and combinations of the books in each case. The order of the books is irrelevant, confirming that permutations were incorrectly applied in earlier calculations.

PREREQUISITES
  • Understanding of combinatorial principles, specifically permutations and combinations.
  • Familiarity with the notation P(n, k) for permutations and C(n, k) for combinations.
  • Basic arithmetic skills for calculating factorials and products.
  • Knowledge of how to categorize items based on distinct characteristics (e.g., language).
NEXT STEPS
  • Study the principles of combinatorial counting in detail.
  • Learn how to apply the P(n, k) and C(n, k) formulas in various scenarios.
  • Explore advanced combinatorial problems involving multiple categories and constraints.
  • Practice solving similar problems to reinforce understanding of language exclusion in arrangements.
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Students studying combinatorics, educators teaching mathematical concepts, and anyone interested in solving combinatorial problems involving multiple categories.

Shoney45
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Homework Statement


Given nine different English books, seven different French books, and five different German books: How many ways are there to mak a row of three books in which exactly one language is missing?




Homework Equations



P(n,k) C(n,k)

The Attempt at a Solution



I broke this up into six cases: Let English books be represented by E, German books by G, and French books by F. My six cases then are:

(2E)F = p(9,2)*7 = 504
(2E)G = p(9,2)*5 = 360
(2F)E = p(7,2)*9 = 378
(2F)G = p(7,2)*5 = 210
(2G)E = p(5,2)*9 = 540
(2G)F = p(5,2)*7 = 420

all of which equals 2412 possibilities.
 
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Hi Shoney45! :smile:
Shoney45 said:
Given nine different English books, seven different French books, and five different German books: How many ways are there to mak a row of three books in which exactly one language is missing?

(2E)F = p(9,2)*7 = 504
(2E)G = p(9,2)*5 = 360
(2F)E = p(7,2)*9 = 378
(2F)G = p(7,2)*5 = 210
(2G)E = p(5,2)*9 = 540
(2G)F = p(5,2)*7 = 420

The order of the books doesn't matter, so it's not p. :wink:

(and where did your 60 come from in the last two? :confused:)
 
tiny-tim said:
Hi Shoney45! :smile:


The order of the books doesn't matter, so it's not p. :wink:

(and where did your 60 come from in the last two? :confused:)

Sorry, but I don't understand what you mean by the 60 in my last two.

Never mind. I just figured out what you meant. That was just bad arithmetic.
 

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