Question

The 14th term of an A.P. is twice its 8th term. If its 6th term is -8, then find the sum of its first
20 terms.

Answer 1

term3 + term8 = 7
a+2d + a+7d = 7
2a + 9d = 7 **

term7 + term14 = -3
a+6d + a+13d = -3
2a + 19d = -3 ***

subtract ** from ***
10d =-10
d = -1