arrangement-P and C

Question

In how many ways 8 persons can be arranged on two round tables consisting of 4 chairs each?

a)720

b)1260

c)2520

d)5040

Comments

can anyone explain this pls. In the solution given below why aren't we multiplying it by 2 for selecting on which table which group is going?? My answer was coming 5040 becoz of that table selction.

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There are two tables. Let them be A and B.

We are selecting 4 people for A. Then 4 people for B.

If we first select 4 people for B, this case will already be part of the above selection as any 4 people out of 8 can go to A or B. This way order in which we fill tables A or B doesn't matter for the total possibilities.

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ok sir thanks samjh gaya mai

Answer 1

Answer should be 8C4x((4 - 1)!)^2 = 2520.
All possible ways of making two groups of 4 people out of 8 people = 8C4.
IN EACH ROUND TABLE, all possible ways of arranging 4 people = (4 - 1)!
Which gives 8C4x((4 - 1)!)^2 = 2520.