Q.11. In how many ways can the letters of the word PERMUTATIONS be arranged if the
            (iii) there are always 4 letters between P and S?
 
                
                  The letters of the word PERMUTATIONS be arranged in such a way that there are always 4 letters between P and S.
Therefore, in a way P and S are fixed. The remaining 10 letters in which 2 T's are present can be arranged in
                                                                                                                                                                                      ways.
Also, P and S can be placed such that there are 4 letters between them in  ways.
Therefore, using the multiplication principle required arrangements