The number of 4 letter words can be formed from the letters of the word ‘INFINITY’ so that 2 are same 2 are different is:

there are total 8 letters in the word INFINITY ,

out of which,3 letters are of one type (i.e., the letter I ), 2

are of second type (i.e., the letter N ) and the remaining 3 are
(i.e., the letters F,T and Y) are each of 1 type.
= 8! / (3!*21*1!*1!*!)
= 3360 
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