# Homework Help: Find the sum of first 28 terms?

1. Aug 13, 2010

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. Aug 13, 2010

### rock.freak667

Re: AP,Gp,Mean

Just sub in the information and get the values for 'a' and 'd' via solving the equations simultaneously.

3. Aug 13, 2010

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

4. Aug 13, 2010

### rock.freak667

Re: AP,Gp,Mean

and why not?

5. Aug 20, 2010

### dharavsolanki

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!

6. Aug 20, 2010