怎麽解這道題?謝謝!

來源: 2009-01-11 11:09:39 [舊帖] [給我悄悄話] 本文已被閱讀:

If upper-case and lower-case letters are considered as different letters,how many six-letter computer passwords are possible
a) with no repeated letters?
b) with at least one capital letters?

Thanks in advance!