I understand how to do regular permutation but when dealing with words, I do not know how to do them. I know the formula is: n!/(n1, n2,...nk). (The n1,n2,...nk being double of the same letters), but I don't understand that. I always though Permutation was nPr = n! / (n - r)! . Can someone explain this to me please?
Here is an example of 1 of the problems thats due friday:
Be sure to explain your answers for each part.
(a) How many distinct four-letter strings can be formed from the letters in UCFFCU? It may help to imagine six tiles with the letters U, C, F, F, C, U, each letter printed on its own tile. A four-letter string is formed by picking any four of these tiles and arranging them in a line.(UCFFCU stands for University of Central Florida Federal Credit Union, by the way.)
(b) How many strings in part (a) are palindromes? (A palindrome is a string that is the same forwards or backwards, such as UCFFCU.)