Answer
The constant of variation is $0.16$.
The direct variation equation is $y=0.16x$.
Work Step by Step
$y=kx$
$y=0.4; x=2.5$
$0.4=k(2.5)$
$\frac{0.4}{2.5}=k$
$0.16=k$
The constant of variation is $0.16$.
The direct variation equation is $y=0.16x$.