Combinations with 4 letters in word STUDENT

[F19]

Any help is appreciated!

1) How many different "words" can be made using the letters in the word STUDENT if 4 of the letters are selected (taking into account repetitions- the 2 T's).

Thanks alot!

 

[mmm4444bot]

How many four-letter permutations are there from seven letters?

How many duplicates are there due to the pair of Ts?

Subtract those from the total.