Thread: combinatorics

Hi,

Please help with this question...

The number of words that can be formed by taking 4 letters at a time out of the letters of the word MATHEMATICS is ______

Originally Posted by kladizkov

The number of words that can be formed by taking 4 letters at a time out of the letters of the word MATHEMATICS is ______

Do you know how to use generating functions?
If so then the answer is rather easy to find.

If not, then this is a problem of different cases.
The is because you have three sets or repeated letters: {M,M,A,A,T,T}.
So you must consider cases of no reparations, one letter repeated, etc.