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Solving equations via substitution

  1. Apr 13, 2012 #1
    I am trying to solve an equation that involves substitution.

    I was given k= 7 in the equation n=k+c
    i was also given n=2^c-1
    I figured that 7+c could be substituted into the equation as n, so I got
    7+c=2^c-1 and therefore c=2^c-8.
    The problem is that the answer I want is c=4...but substituting 4 as C does not give me a correct answer. Any help would be greatly appreciated.
    Thank you
  2. jcsd
  3. Apr 13, 2012 #2

    Stephen Tashi

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    Science Advisor

    Maybe the probem should say n = k + 2c
  4. Apr 13, 2012 #3
    This pertains to hamming codes, so n is the total number of bits, k is the amount of information digits and c is the amount of check digits. I was given another example aswell. This example says: Suppose there are four information digits.
    Then n=4+c
    and n=2^c-1
    then 4+c=2^c-1
    hence c=2^c-5
  5. Apr 14, 2012 #4

    Stephen Tashi

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    Science Advisor

    The inequation I see on the web for hamming codes is [itex] n \le 2^c -1 [/itex]
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