To log on to a certain computer account, the user must type in a 4-letter password. In such a password, no letter may be repeated, and only the lower case of a letter may be used. How many such 4-letter passwords are possible? (There are 26 letters in the alphabet.) In such a password, no letter may be repeated, and upper case or lower case of a letter may be used. How many such 4-letter passwords are possible? (There are 26 letters in the alphabet.)
+57 26*25*24*23=358800 without any uppercase letters and no repeated letters and 52*51*50*49= with uppercase letters
