# Simple permutations?

• January 6th 2011, 06:48 AM
berto
Simple permutations?
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 $26^3$, but it not answer.

thank you!
• January 6th 2011, 06:56 AM
Plato
Quote:

Originally Posted by berto
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 $26^3$

You are correct. As posted the answer is $26^3$.
Did you post the exact wording?
• January 6th 2011, 07:30 AM
Soroban
Hello, berto!

Quote:

How many three-letter combinations can be made using the US alphabet.
Letters can be repeated.

Answer in book: 18,278

I agree with Plato . . . check the original wording.

I bet it says "combinations with up to three letters".

Then the answer is: . $26 + 26^2 + 26^3 \:=\:18,\!278$