Problem: In how many ways can these letters EFGHIEFGHI be arranged if the same letter musn't appear next to each other?
since we have 2 E's, F's, G's, H's and I's... The formula should be
10!
------------- = 113400 ways
2!2!2!2!2!
Then I combine similar letters [EE]FGHIFGHI for 5 letters
9!x5
-------- = 113400 ways
2!2!2!2!
That's where i get stumped... need help... XD
If that is true, then I must wonder why you are asked to do this problem?
Inclusion-Exclusion Principle -- from Wolfram MathWorld