Question: 2013 Fall Midterm - 3
A password consists of 6 or 7 characters, each character being an uppercase or a lowercase letter. A password must contain at least one uppercase letter. How many passwords are there?
(a)
$52^{6} + 52^{7} - 26^{6} - 26^{7}$
(b)
$52^{6} + 52^{7}$
(c)
None of the above.
(d)
$26 \cdot 52^{5} + 26 \cdot 52^{6}$