Results 1 to 4 of 4
Like Tree2Thanks
  • 1 Post By romsek
  • 1 Post By Plato

Math Help - How many passwords are possible?

  1. #1
    Newbie
    Joined
    Apr 2014
    From
    USA
    Posts
    5

    How many passwords are possible?

    Hi everybody,

    I'm a bit confused about this one problem in my Barrons SAT II Math book. It reads, "A code consists of two letters of the alphabet followed by 5 digits. How many such codes are possible?"

    Barrons gives the answer as (26)(26)(10)(10)(10)(10)(10)= 67,600,000 possible codes. I am confused because I think this method would produce repeat answers, and I think I would have to divide it by something, but I'm not sure what. (I"m not sure how to describe how I am confused, I just feel like this method would produce for example aa54865 twice and not take into account that aa is the same no matter what order the a's are placed in... Am I making sense?) Anyways, is Barrons right or am I? And if I am right, what would I need to divide by to get the right answer?

    Thank you very much!
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Joined
    Nov 2013
    From
    California
    Posts
    2,789
    Thanks
    1147

    Re: How many passwords are possible?

    26 ways for the first letter,
    26 ways for the second letter,
    10 ways each for the 5 digits

    $26^2\cdot 10^5=67.6$ million codes. Barrons is correct. If you were just looking for a group of 2 letters and 5 digits where order didn't matter you would be correct but that's not the case here. Order matters in a code.
    Thanks from precalc
    Follow Math Help Forum on Facebook and Google+

  3. #3
    MHF Contributor

    Joined
    Aug 2006
    Posts
    18,957
    Thanks
    1780
    Awards
    1

    Re: How many passwords are possible?

    Quote Originally Posted by precalc View Post
    I'm a bit confused about this one problem in my Barrons SAT II Math book. It reads, "A code consists of two letters of the alphabet followed by 5 digits. How many such codes are possible?"
    Barrons gives the answer as (26)(26)(10)(10)(10)(10)(10)= 67,600,000 possible codes. I am confused because I think this method would produce repeat answers!
    Why are you confused? Do you understand the multiplication rule?
    You want to do two thing that can be done in twenty-six ways followed by an action that can be done in ten ways five times.
    Thanks from precalc
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Newbie
    Joined
    Apr 2014
    From
    USA
    Posts
    5

    Re: How many passwords are possible?

    Ohhh, I understand it now! Thank you very much Plato and romsek!
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Passwords problem
    Posted in the Statistics Forum
    Replies: 2
    Last Post: May 18th 2013, 10:14 AM
  2. Eight character passwords
    Posted in the Discrete Math Forum
    Replies: 2
    Last Post: May 16th 2010, 07:45 AM
  3. Counting passwords
    Posted in the Discrete Math Forum
    Replies: 1
    Last Post: May 14th 2010, 04:27 PM
  4. Replies: 2
    Last Post: January 17th 2009, 03:40 AM

Search Tags


/mathhelpforum @mathhelpforum