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# In how many ways can 5 persons be seated around a circular t

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In how many ways can 5 persons be seated around a circular t [#permalink]  14 May 2019, 00:40
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Question Stats:

41% (00:04) correct 58% (00:24) wrong based on 12 sessions
In how many ways can 5 persons be seated around a circular table?

(A) 5

(B) 24

(C) 25

(D) 30

(E) 120
[Reveal] Spoiler: OA

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Re: In how many ways can 5 persons be seated around a circular t [#permalink]  15 May 2019, 05:19
Expert's post
Quote:
In how many ways can 5 persons be seated around a circular table?

To avoid using Combination or Permutation notation, you can always just consider the following steps to manually calculate the scenario:

1) Draw a ____ for each selection to be made and label any dictated restrictions for the selection.
In this case there will be a selection of five seats:
Seat 1 | Seat 2 | Seat 3 | Seat 4 | Seat 5

2) Insert the number or available options at moment of selection one blank at a time.
In this case: Seat 1 = 5 | Seat 2 = 4 | Seat 3 = 3 | Seat 4 = 2 | Seat 5 = 1

3) Now, for each seat consider - does order matter? If order does matter, there is no need to cancel out equivalent options, so just multiply by the number of options available for the selection. However, if order does not matter, you must first divide the number of available options by the number of equivalent available _____s at the moment of selection.

So, in this case with a circular table, in the selection of the first seat, order does not matter since the arrangement is based on the perspective of whomever is seated first regardless of where they sit. So, for seat 1 you must divide the 5 available people by the 5 available equivalent seats.

Once the perspective is established by seating the first person, however, order does matter so you must not divide the remaining available options leaving 4 x 3 x 2 x 1 for the remaining seats.

4) Finally, calculate. When selecting this AND that - multiply, but first reduce any present fractions to simplify the calculation. So, in the first seat the 5/5 can be canceled out to = 1, so there remain 4 x 3 x 2 x 1 = 24 ways to seat these five people around a circular table, which matches choice B.
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Re: In how many ways can 5 persons be seated around a circular t [#permalink]  22 Aug 2019, 18:23
Carcass wrote:
In how many ways can 5 persons be seated around a circular table?

(A) 5

(B) 24

(C) 25

(D) 30

(E) 120

I'm sad to admit that I solved this one but memorization of how to arrange n people around a table. Turns out it's (n-1)!

so (n-1)! = (5-1)! = 4! = 4*3*2*1 = 24.

So B.
Re: In how many ways can 5 persons be seated around a circular t   [#permalink] 22 Aug 2019, 18:23
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