Question

If $S=\frac{n}{2}[2a+(n-1\left)d\right]$ ; find $d$ , when $a=8,S=380$ and $n=10$.

• A. $7\frac{1}{6}$
• B. $4\frac{5}{2}$
• C. $2\frac{1}{6}$
• D. $6\frac{2}{3}$

Answer 1

The correct option is D $6\frac{2}{3}$

We know, $S=\frac{n}{2}[2a+(n-1\left)d\right]$

Given, $a=8,S=380$ and $n=10$

$\therefore 380=\frac{10}{2}\left(2\right(8)+9d)$

$380=5(16+9d)$

$300=45d$

$\therefore d=\frac{300}{45}$ $=6\frac{30}{45}$ $=6\frac{2}{3}$