(i) There are 11 letters of which 2 are of 1 kind, 2 are of another kind, 2 are of the 3rd kind
Total number of arrangements = \(\frac{11!}{2!2!2!}\) = 4989600
(ii)
There are 10 spaces to be filled by 10 letters of which 2 are of 3 different kinds
Number of arrangements = \(\frac{10!}{2!2!2!}\) = 453600
(iii)
There are 10 spaces to be filled by 10 letters of which 2 are of 2 different kinds
Number of arrangements = \(\frac{10!}{2!2!}\) = 907200