Q. If the sum to first $n$ terms of the AP 2, 4, 6,… is 240, then the value of $n$ is
A) 14
B) 15
C) 16
D) 17
Explanation
(b)
$\frac{n}{2}\left\lbrack 2 \times 2 + (n - 1) \times 2 \right\rbrack = 240$
$\Rightarrow \ n(2 + n - 1) = 240$
$\Rightarrow \ n(n + 1) = 15 \times 16$
$\Rightarrow n = 15$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.