Can any check out this one?

A password for the computer is a string of digits

0, 1, 2, 3, 4, 5, 6, 7, 8, 9

and/or letters

a,b,c,. . . ,x,y,z

(there are 26 different letters). The password must obey the following

rules:

(a) the length of the password must be exactly 8 characters;

(b) the password must contain at least one digit, and no more than

three digits.

What is the number of different passwords you can form?

I think number of different passwrds are

10x26! + 10x10x25! +10x10x10x24!