Q4 of 105 Page 146

The first and the last terms of an AP are 17 and 350 respectively. If the common difference is 9, how many terms are there and what is their sum?

Given first term (a) = 17, last term (an) = 350

Common difference (d) = 9


an = a + (n-1) d


350 = 17 + (n-1) 9


333 = 9(n-1)


37 = n-1


n = 38.


Sum of the series (sn) = [2a + (n-1) d]


= ( 2×17 +(38-1)9)


= 19 × 367


= 6973


More from this chapter

All 105 →
3

In an AP :

given an = 4, d = 2, sn = -14. Find n and a

 3

In an AP :

given l = 28, sn = 144 and there are 9 terms Find and a

 5

Find the sum of first 51 terms of an AP whose second and third terms are 14 and 18 respectively.

 6

If the sum of first 7 terms of an AP is 49 and that of 17 terms is 289, find the sum of first n terms.