I have seen the problem in this forum about 6 number 1,1,2,2,3,3 to be arranged in a line with no same adjacent numbers. The solution is 30. But what happens if there are 8 number 1,1,2,2,3,3,4,4? Are there any general rules and quick ways to solve? I have tried to 8!/(2!2!2!2!)- 4 pairs -3 pairs-2pairs - 1pair, but the computations are too cumbersome....any good ways to solve? please help