Answer
$y=0.1\cdot xz$
Work Step by Step
If $y$ varies jointly as $x$ and $z,$ then $y=kxz.$
Given $x=5, z=4, y=2$, we find k
$2=k\cdot 5\cdot 4$
$ 2=20k\qquad$... divide with $20$
$k=\displaystyle \frac{2}{20}=0.1$
$y=0.1\cdot xz$
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