Question

If 12th term of the ap is -13 sum of its first four term is 24. what is sum of first ten terms?

Answer 1

$t(12) = - 13 \\ a + 11d = - 13$

S(4)= 24

$2(2a + 3d) = 24 \\ 2a + 3d = 12$
By solving
$19d = - 38 \\ d = - 2$
$a = 9$
$s(10) = 5(2a + (n - 1)d) \\ = 5(18 + 9( - 3)) \\ = 5( - 9) \\ = - 45$