Hi everyone, I have a problem whose solution I don't understand.

Find the number of five-letter words that use letters from {A,B,C} in which each letters occurs at least once.

Solution:

3^5 -2^5 -2^5 -2^5 +1 +1 +1 = 150

But, my solution is 3^5 -2^5 -2^5 -2^5 -1 -1 -1 = 144

I don't know why I'm wrong. Please, help me to explain it. Thank you very much.