Question

If 12th term of an AP is 12 and the sun of its first four term is 24 what is sum of its first four terms?

Answer 1

$a12 = a + 11d = 12 ......(1)$
and sum of first 4 terms is 24
$\frac{n}{2} \: (2a + (n - 1)d) = 24 \\ \frac{4}{2} (2a + 3d) = 24 \\ 2a + 3d = 12...(2)$
equation ( 1 ) × 2
2a + 22d = 24.....(3)
eq(3) - eq(2)
19d=12
d=12/19
put d in (1)

Answer 2

Hey Mate!!

Please find the answer in the attachments...