How many three-letter “words” (strings of letters) can be formed using the 26 letters of the alphabet if repetition of letters...

Question

How many three-letter “words” (strings of letters) can be formed using the 26 letters of the alphabet if repetition of letters (a) is allowed? (b) is not allowed?

Answer 1

these are permutations

for example, ABC is different from CBA

a) 26*26*26=17,576

b) 26*25*24=15,600