Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Help for combinatorial question?

  1. Mar 18, 2009 #1
    a "codeword" from the alphabet A={0,1,2,3) is said to be legitimate if it contains even number of zeros. Thus for instance the codeword 31020 is legitimated and 0002 is not. How many n - letter codewords are legitimated ?
     
  2. jcsd
  3. Mar 18, 2009 #2

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    Hi erogol! :wink:

    Show us what you've tried, and where you're stuck, and then we'll know how to help! :smile:
     
  4. Mar 18, 2009 #3
    i have no sense to solve it i just know answer is 2^(2n-1) + 2^n -1
     
  5. Mar 18, 2009 #4

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    ok, start by making a sum over all possible (even) numbers of 0s …

    the total number of legitimated words is ∑ what ? :smile:
     
  6. Mar 18, 2009 #5

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    So you are not even going to try?
     
  7. Mar 18, 2009 #6

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    Are you talking to me? :biggrin:
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook