Circle Permutations: 7 People, A Not Next to B

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SUMMARY

The problem of seating 7 people around a table with the condition that person A does not sit next to person B can be solved using combinatorial principles. The total arrangements without restrictions is calculated as 6! (720). By seating A first, there are 5 valid options for the person to A's right and 4 for A's left, leading to 20 configurations for A's neighbors. After seating A and ensuring B is not adjacent, the remaining 4 people can be seated in 4! (24) ways, resulting in a total of 480 valid seating arrangements where A and B are not next to each other.

PREREQUISITES
  • Understanding of factorial notation and permutations
  • Basic knowledge of combinatorial mathematics
  • Familiarity with circular permutations
  • Ability to apply restrictions in combinatorial problems
NEXT STEPS
  • Study circular permutations in depth
  • Learn about combinatorial restrictions and their applications
  • Explore advanced counting techniques in discrete mathematics
  • Practice solving similar seating arrangement problems with different constraints
USEFUL FOR

Mathematics students, educators, and anyone interested in combinatorial problem-solving, particularly in seating arrangements and permutations.

Cyborg31
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Homework Statement


7 people around a table, how many ways of seating if A does not want to be next to B?


Homework Equations



(n-1)!

The Attempt at a Solution



Well I know the number of ways to get 7 people around a table is 6! but not sure how to solve it if A does not want to be next to B.
 
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Seat A first anywhere at the table. There are 6 people left to seat but one of those, B, cannot be seated next to A. That means there are 5 people who could be seated on A's right side. After that choice is made, there are 4 people who could be seated on A's left side. Once you have people seated on either side of A, you can put B back into the "mix". There are now 4 people to choose the next person to seat from, then 3, then 2, then 1.
 

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