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Find the sum of first 28 terms?

  1. Aug 13, 2010 #1
    1. The problem statement, all variables and given/known data
    sum of first 11 terms of Ap is 17 and sum of first 17 terms is 11
    find the sum of first 28 terms?


    2. Relevant equations

    Sum=n/2[2a+(n-1)d]


    3. The attempt at a solution
    i tried solving it by using obove formula but i am not able to do so as the value of d is coming in fraction
     
    Last edited by a moderator: Jul 22, 2014
  2. jcsd
  3. Aug 13, 2010 #2

    rock.freak667

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    Re: AP,Gp,Mean

    Just sub in the information and get the values for 'a' and 'd' via solving the equations simultaneously.
     
  4. Aug 13, 2010 #3
    Re: AP,Gp,Mean

    i tried but after soving the equations, value of d is coming in fraction.and the common difference cannot be a fraction number
     
  5. Aug 13, 2010 #4

    rock.freak667

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    Re: AP,Gp,Mean

    and why not?
     
  6. Aug 20, 2010 #5
    Re: AP,Gp,Mean

    Yes, why cannot the common difference be a fraction? Are 1, 1.25, 1.5, 1.75, 2 not n AP?

    Hey Niraj, keep posting your dobts on PF here, we need a lot of warming up to do!
     
  7. Aug 20, 2010 #6

    statdad

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    Re: AP,Gp,Mean

    The common difference can be a whole number, fraction, irrational number, as well as positive or negative. Finding a fraction most certainly is not an indication of an error on your part.
     
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