I think it in right forum. It's in university, but title of class is Basic Statistic.

I'm supposed to find out how many three-letter combinations i can make using the US alphabet. letters can be repeated...

so, it's from AAA to ZZZ

I not sure where to begin problem. answer in book: 18,278

i though it was $\displaystyle 26^3$, but it not answer.

thank you!