Question

In an ap the 12th term is -13 and the sum of its first four terms is 24.find the sum of its first 10 terms.

Answer 1

Its an easy one. The answer is 0.

Answer 2

a12 = -13
a + 11d = -13
a = -13 - 11d -------1

Sum of first 4 terms
a + a + d + a + 2d + a + 3d = 24
4a + 6d = 24
2a + 3d = 12
2 ( -13 -11d ) + 3d = 12
-26 -22d + 3d = 12
-19d = 38
d = -2
Putting in 1
a = -13 - 11d
a = -13 - 11(-2)
a = -13 +22
a = 9

Sum of 10 terms Sn=n/2(2a+(n-1)d) Sn=10/2(2(9)+(10-1)(-2)) S=5(18-18) S=0 Plz mark as the brainleist