Question

how many different 10-letter words (real or imaginary) can be formed from the following letters P,Z,X,N,W,T,Z,I,I,X?

Answer 1

using stars and bars method, you have 10 letters but 3 of them are repeat one time, so in fact you have just 7 different letters, which are P, Z, X, N,W,T,I. so you have 7 stars and need 6 bars to separate them and you must choose 10 letters. that means you have 16 items to arrange in 6 bars, the compute is (16 choose 6) = 8008 .