JCCDQBHWHCB019 Combinatorics : Circular Permutations

Suggested Approach and Solution:-

     Draw a diagram.  Let’s assume that the special woman (W*) is at the 12 o’clock reference position.  [If not, we can always rotate our heads or rotate the table so that she is.] 

 

Together with the two lucky(?) men M₁ and M₂, they form one entity.  There are ³C₂ x 2!

= ³P₂ = 6 ways to choose and arrange these two men to sit besides this special woman.  The other 4 persons can arrange themselves relative to the reference entity in 4! = 24 ways (this is same as (5 – 1)! or ^5! / ₅).  Hence the number of ways = 6 x 24 = 144.