**Q) **The sum of first 15 terms of an A.P. is 750 and its first term is 15. Find its 20th term.

**Ans: **

Given that a = 15 and Sum of 15 terms of an A.P. S_{15 }= 750

We know that sum of n terms of an A.P. S_{n }= (2a + (n-1) d)

S_{15 }= (2 x 15 + (15 – 1) d) = 750

15 (30 + 14 d ) = 750 x 2

30 + 14 d = 100

14 d = 70

d = 5

Next, we know that n^{th} term of an A.P. = a + (n-1) d

Hence, 20^{th} term, N_{20} = 15 + (20 – 1) x 5 = 15 + 19 x 5 = 110

**Therefore, the value of 20 ^{th} terms is 110.**