We have been given the following question for our mock exam:
Each student has a password, which is 6 characters long and each character is either a digit or a lower case letter. Each password must contain at least ONE letter. How many possible passwords are there?
26 lower case letters 10 digits 6 characters long At least one letter
The way I understood, is that it would be easier using inclusion-exclusion, therefore:
$36^6 - 10^6 $ = 2175782336
However another student mentioned it would be:
$36^6 - 10^5 $ = 2176682336
And I also heard:
$36*36*36*36*36*26$ = 1572120576
I think the word "at least ONE letter" is throwing me off a bit. Would anyone mind explaining this to me, please?