Question 74421
This problem is rather ambiguous. Do you mean 11 letter words or all words consisting of 2 letters or more(up to 11)?. 

If they are 11-letter words, then:

There are 11 letters in the word MATHEMATICS. But, there are some letters repeated. There are 2 T's, 2 E's, and 2 A's 

Therefore, the number of possible arrangements is:

{{{11!/(2!2!2!)=11!/8=39916800/8=4989600}}}

The problem gets more complicated if you must count all words, regardless of size, up to 11 letters.