kenneth rosen

Question

Each user on a computer system has a password, which is six to eight characters long, where each character is an uppercase letter or a digit. Each password must contain at least one digit.how many possible passwords are there?

I understand sum rule will be applied adding P6+P7+P8

my doubt is how we will ensure password will contain one digit?

in rosen solution P6 = 36^6 - 26^6 why they did like this?

Answer 1

No of alphabets : 26

No of digits : (0 to 9)

total characters : 10+26 = 36

P6 =  Total no of ways to create a password with 36 characters - no of ways in which  all 6 characters are   alphabets  

     =  (36)⁶ - (26)⁶

Similarly we do with P7 and P8

then add p6+p7+p8

 

 

Comments

okay i got it just edit  no of digits : 0 to 9