Results 1 to 2 of 2

Math Help - How many bit strings of length 27 are there...?

  1. #1
    Newbie
    Joined
    Jul 2010
    Posts
    1

    How many bit strings of length 27 are there...?

    How many bit strings of length 27 are there such that:

    a. the bit string corresponding to the last twelve positions contain exactly seven 0

    b. the bit string has at least fifteen 0 and at least ten 1, also must have the bit string corresponding to the first nine positions contains six 1and the bit string corresponding to the last twelve positions contain a maximum of ten 0.

    c. the bit string corresponding to the first ten positions contain exactly eight 1 and a bit string corresponding to the last fifteen positions contains (or does not contain) the string as a sub-string 1011101


    Help me please!!!
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Senior Member
    Joined
    Apr 2009
    Posts
    308
    Hi,

    I will attempt a.

    For the last 12 positions there are \binom{12}{7} ways to pick the 0's, once the 0's are fixed, the 1's fall naturally into position.

    Then for the first 15 positions there are 2 choices for each positions, either a 1 or 0, thus there are 2^{15} choices for the 1st 15 positions.

    Thus in total we have \left(2^{15}\right)\binom{12}{7} bit strings.

    I would really like to know if this is correct though, could someone confirm? Thanks.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. how many length-k strings can be made
    Posted in the Discrete Math Forum
    Replies: 1
    Last Post: September 17th 2009, 04:31 AM
  2. How many bit strings of length 10....
    Posted in the Statistics Forum
    Replies: 1
    Last Post: February 22nd 2009, 06:52 PM
  3. strings
    Posted in the Statistics Forum
    Replies: 10
    Last Post: January 17th 2009, 01:35 PM
  4. how many bit strings of length 10 ...
    Posted in the Discrete Math Forum
    Replies: 4
    Last Post: October 20th 2008, 04:04 PM
  5. how many bit strings are there of length 6 or less
    Posted in the Discrete Math Forum
    Replies: 1
    Last Post: October 15th 2008, 10:01 AM

Search Tags


/mathhelpforum @mathhelpforum