What should be added to $6\frac{7}{15}$ to get $8\frac{1}{5}$?

Let $x$ be added to $6\frac{7}{15}$ to get $8\frac{1}{5}$
$\Rightarrow 6\frac{7}{15}+x=8\frac{1}{5}$

$\Rightarrow x=\frac{7}{15}-8\frac{1}{5}$

$\Rightarrow x=\frac{97}{15}-\frac{41}{5}$

L.C.M. of $5$ and $15$ is $15$

$\Rightarrow x=\frac{97}{15}-\frac{41}{5}\times \frac{3}{3}$

$\Rightarrow x=\frac{97}{15}-\frac{123}{15}$

$\Rightarrow x=-\frac{26}{15}$

$\Rightarrow x=-1\frac{11}{15}$

Therefore, $-1\frac{11}{15}$ is the required number