Question

If the 12th term of an ap is -13 and the sum of first four terms is 24. What is the sum of first 10 rerms

Answer 1

a+ (12-1)d = -13. ........
a + 11d = -13 ×4 is. 4a + 44d = -52.......eq 1

4/2(2a+ (4-1 ) d )= 24 here n=4 ............eq2
then : 2 ( 2a + 3d ) =24 ..
4a + 12d = 24 ......eq3
substitute 1 &3 eq-
we get d = 9/4
a = -151/4
to find first 10terms
use the formula