What is the sum of the first 9 terms of an arithmetic progression if the first term is 7 and last term is 55?
A. 219 B. 279 C. 231 D. 137 Answer: Option BShow Answer
Solution(By Apex Team)
$\begin{aligned}S_n&=\frac{n}{2}(a+l)\\
S_9&=\frac{9}{2}(7+55)\\
S_9&=\frac{9}{2}\times62\\
S_9&=9\times31\\
&=279\end{aligned}$
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