Six persons A , B , C , D , E and F are to be seated at a circular table facing towards the centre. Then the number of ways that can be done if A must have either E or F on his immediate right and E must have either F or D on his immediate right, is

Step-by-step solution

There are two cases, I is to the immediate right of A . Number of ways E can fill = 3 ways E cannot take sit on the left of A as there will be no space. Number of ways D can fill = 1 ways The remaining seats can be filled in 2 ways. The total numbers of ways are 3 × 1 × 2 = 6 The required number of ways are 12 + 6 = 18