Question

In an AP if 12th term is - 13 and the sum of first four term is 24.What is the sum of the first 10 terms.

Please answer this question....

Answer 1

a12= -13 = a+11d
a = -13-11d
s4=24 = 4/2 {2a + (4-1)d}
24 = 2 {2a + 3d}
12 = 2a + 3d
12 = 2(-13-11d) + 3d
12 = -26-22d+3d
12+26 = -19d
38 = -19d
-2 = d
a = -13-11d
a = -13-22
a = -35
s10 = 10/2{2(-35) + (10-1)-2}
= 5 {-70-18}
s10 = 5× -88
s10 = -440

Answer 2

I hope my answer is wright.