Question

If sum of $n$ terms of A.P. is $476,$ last term $=20,n=17$, then the first term is :

• A. $32$
• B. $34$
• C. $36$
• D. $38$

Answer 1

The correct option is C $36$

Here, $S_n=476,n=17,l=20$

$S_n=\frac{n}{2}(a+l)............[\because l=a+(n-1)d]$

$\Rightarrow 476=\frac{17}{2}(a+20)$
$\Rightarrow a+20=\frac{476\times 2}{17}$
$\Rightarrow a+20=56$
$\Rightarrow a=36$