Since there are 11 letters of the word MISSISSIPPI, then the number of words could be arranged is 11! ways.
However, there are 4 I's, 4 are S's and 2 are P's.
Then, we need to eliminate the number of the repeated words.
Then the number of words is 11!/2!4!4! = 34,650
If There are n different letters, they could be permuted in nPn = n! different arrangements.
If out of n things p of them of them are alike, another q of them are them are alike and still another r of them are alike then the number of arragements is equal to n!/(p1*q!*r!).
In mississipi , the alphabets are 11. there are 4 letters s alike. Two letters are i's alike. So the number of permutations of 11 letters of which 4 are s alike and another 2 are i alike is = 11!/(4!*2!) = 831600