I have the answer but how should it be solved ? This way 1P1*1P1*6P6 ?7 boys are seated in a row. Calculate different ways in which this can be done if 2 particular boys A and B have exactly 3 other boys between them.

Question

Answer

720

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- Jun 8th 2014, 12:29 AMhaftakhanPermutation Question
**I have the answer but how should it be solved ? This way 1P1*1P1*6P6 ?**7 boys are seated in a row. Calculate different ways in which this can be done if 2 particular boys A and B have exactly 3 other boys between them.

Question

**Answer**

720 - Jun 8th 2014, 01:53 AMDevenoRe: Permutation Question
If B is 3 chairs to the right of A, A can only be seated in chair 1,2, or 3. Otherwise, B is to the left of A, and the possible positions of A and B are switched. That gives 6 possible ways to seat A and B:

A---B--

-A---B-

--A---B

B---A--

-B---A-

--B---A

For each of these ways there are 5! = 120 ways to seat the remaining 5 boys. That gives 6*(5!) = 6! = 720 possible ways to seat the 7 boys under the restrictions listed.