the sum of the first four terms of an arithmetic sequence is 34 and the sum of the next four terms is 146. find the sum of the 9th and 10th terms

Question

anonymous · Answer

Shall we work together on this?

anonymous · Answer

yeah sure

ujjwal · Answer

Sum of AP series is given by$$S=\frac{n}{2}(2a+(n-1)d)$$You have sum of first 4 terms=34 and sum of next 4 terms=146..
So, sum of first 8 terms=34+146=180

So, when n=4, S=34
When n=8, S=180
Replace those values in above relation!
And then you will get two equations.. Solve for a and d..

Now put n=10 (also put obtained values of a and d)
you will get sum up to 10th term! 
Since the sum of first 8 terms is 180, Subtracting 180 from sum of 10 terms will give you sum of 9th and 10th term!