If upper and lower case letters in a 6 letter passwords

Hi, can someone hwlp me with this question?

If upper and lower case letters are considered as different letters, how may 6 letter passwords are possible if

a) there are no repeating letters
b) with at least one capital


a)

52*51*50*49*48*47
=14 658 134 400

but the answer is 19 770 609 664

b)

26C1*26C5
26C2*26C4
26C3*26C3
26C4*26C2
26C5*26C1
26C6*26C0

=19 799 390

but the answer is 19 461 693 888


Thanks

I agree with you about part a.
You really have had trouble with that answer key!

lol, thanks Pka

For part (b) take the total of all lower case passwords from the total.
\(\displaystyle P(52,6) - P(26,6)\)