I cant remember how to solve these.
A computer password consists of eight letters. How many passwords are possible? Assume there is no difference between lower-case and upper-case letters.
Please help!
What we are dealing with here is a permutation.
Recall that $\displaystyle _nP_r=\frac{n!}{(n-r)!}$ where $\displaystyle r\leq n$.
Since the password can contain only letters, and we are to assume that there is no difference between lower and upper case we must let $\displaystyle n=26$ [if there was a difference between upper and lower case, $\displaystyle n=52$]. Since the password can only be 8 letters long, let $\displaystyle r=8$.
So we see that we now have $\displaystyle _{26}P_8=\frac{26!}{18!}$
Can you take it from here?
--Chris