permutations (password problem)
Can any check out this one?
A password for the computer is a string of digits
, 1, 2, 3, 4, 5, 6, 7, 8, 9
a,b,c,. . . ,x,y,z
(there are 26 different letters). The password must obey the following
(a) the length of the password must be exactly 8 characters;
(b) the password must contain at least one digit, and no more than
What is the number of different passwords you can form?
I think number of different passwrds are
10x26! + 10x10x25! +10x10x10x24!