Joe wants to find all the four-letter words that begin and end with the same letter, and this letter does not appear in the middle. How many combinations of letters must he examine? A word is any sequence of letters, such as MTHM, and does not have to be English. (You can use a calculator for this problem.)
There are 26 choices for the first letter, 26 for the second, and 26 for the third. The fourth letter is automatically determined by the first letter, so our answer is 26^3 = 17576. Hope that helps!