Question 134852
The number of letters is 10. But 3 sets show up twice.

If there are  n objects with  n1  duplicates of one kind,  n2  duplicates of a second kind, ...,  nk duplicates of a  kth  kind, then the number of  distinguishable permutations of these  n objects is

          n!/(n1!n2!...nk!)
see --> http://www.ltcconline.net/greenl/Courses/103B/seqSeries/FACTORI.HTM

We get {{{10!/(2!*2!*2!)}}}
{{{10!/8}}}