#### Answer

The constant of variation is $4$.
The inverse variation equation is $y=\frac{4}{x}$.

#### Work Step by Step

$y=\frac{k}{x}$
$y=\frac{1}{10}; x=40$
$\frac{1}{10}=\frac{k}{(40)}$
$\frac{1}{10}\times40=k$
$4=k$
The constant of variation is $4$.
The inverse variation equation is $y=\frac{4}{x}$.