1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: A password with 8 characters, consisting of Upper case/Lower Case &0-9

  1. Aug 13, 2014 #1
    1. The problem statement, all variables and given/known data

    I am a helping out a friend who is studying Maths at uni, not much help really because I did my degree 10 years ago. I am stuck on a question I was hoping for someone help with the working out:

    A password consist of 8 characters from Uppercase letters, U, lowercase letters L and Digits 0-9, D.

    How many passwords consist of at least one character from U,L & D

    I interpreted this question that it would have to inlcude ULD in the password.

    Anyway I know there are more cases but I think this is wrong anyway - any suggestions will be appreciated.
    2. Relevant equations

    3. The attempt at a solution

    7 D + 1 U/L = 10^7 x 52 x 8c1
    7 U + 1 D/L = 26^7 x 36 x 8c1
    7 L + + 1 D/U = 26^7 x 36 x 8c2
    6 D + 2U = 10^6 X 26^2 x 8c2
    6 D + 2L = 10^6 X 26^2 x 8c2
    6 U + 2D = 26^6 x 10^2 x 8c2 x 2(for L)
    6 U + 2L = 26^6 x 26^2 x 8c2

    Then 1 - (the answer above) is 1.9983 x 10^14
  2. jcsd
  3. Aug 13, 2014 #2


    User Avatar
    Gold Member

    Hm ... how about, for example, 4D + 2L + 2U? Does that not meet the criteria? In other words, I think you have specified the MINIMUM amount, not the actual amount.

    Also, with your interpretation of one each, I don't see how 6D + 2U, for example, would meet the criteria.
  4. Aug 13, 2014 #3
    I though that 6D + 2U would suit because then I am taking the answer away from 1 so I actually want the opposite of 6D+2U ?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted