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Math Help - 1 combination problem

  1. #1
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    1 combination problem

    Thank you in advance. please if possible, explain for me, so i can solve other problems by myself
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  2. #2
    ddt
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    Quote Originally Posted by Narek View Post
    Thank you in advance. please if possible, explain for me, so i can solve other problems by myself
    A 'bit' is a 0 or a 1 (as in computers)
    A 'string' is just another word for a sequence.
    So a 'bit string of length 10' is a sequence of 10 bits. Example: 0010110100
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  3. #3
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    Quote Originally Posted by ddt View Post
    A 'bit' is a 0 or a 1 (as in computers)
    A 'string' is just another word for a sequence.
    So a 'bit string of length 10' is a sequence of 10 bits. Example: 0010110100
    uhum. i understand. but this is not answer to my question
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  4. #4
    ddt
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    Quote Originally Posted by Narek View Post
    uhum. i understand. but this is not answer to my question
    OK, but it wasn't clear what part of the problem you didn't understand.

    So, taking the first of your questions:

    "How many bit strings of length 10 have exactly three 0s?"

    is equivalent to asking: in how many ways can I make a set of 3 positions out of 10? (the positions being the positions in the bit string where the 0s occur - the other 7 positions then have 1s).

    Can you answer that question?

    Hint: Combinations; Binomium of Newton.
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  5. #5
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    I ANSWERED IT!

    i tried to answer them. is these true?


    a) C(10,2)

    b) C(10,5)

    c) C(10,7) + C(10,8) + C(10,9) + C(10,10)

    d) C(10,3) + C(10,4) + C(10,5) + C(10,6) + C(10,7) + C(10,8) + C(10,9) + C(10,10)

    Thank you
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  6. #6
    ddt
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    Quote Originally Posted by Narek View Post
    i tried to answer them. is these true?


    a) C(10,2)

    b) C(10,5)

    c) C(10,7) + C(10,8) + C(10,9) + C(10,10)

    d) C(10,3) + C(10,4) + C(10,5) + C(10,6) + C(10,7) + C(10,8) + C(10,9) + C(10,10)

    Thank you
    (a) is C(10, 3) - I guess that's a typo? For the rest, it's correct yes.
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