Q. 7th term of an AP is 40. Then, the sum of first 13 terms is
A) 520
B) 53
C) 2080
D) 1040
Explanation
(a)
Since, $T_{7} = a + 6d = 40$ …(i)
and $S_{13} = \frac{13}{2}\lbrack 2a + 12d\rbrack$
$= 13\lbrack a + 6d\rbrack$
$= 13 \times 40 = 520$ [from Eq. (i)]
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.