In an A. P, the sum of first ten terms is - 150 and the sum of next 10 terms is - 550. Find the A. P

S10 = - 150;

the sum of next 10 terms = S20 - S10 = > - 550 = S20 + 150 = > S20 = - 700;

S10 = - 150 = > 2a1 + 9r = - 30;

S20 = - 700 = > 2a1 + 19r = - 70;

Then 10r = - 40 = > r = - 4, and, 2a1 - 36 = - 30 = > 2a1 = 6 = > a1 = 3;