Express the following statement as a formula:
w varies jointly with square root of y and z squared and inversely as x cubed.
This means that $\displaystyle w$ is a function directly proportional to $\displaystyle \sqrt{y}$, $\displaystyle z^2$ and $\displaystyle \frac{1}{x^3}$
$\displaystyle w = k \times \frac{z^2 \, \sqrt{y}}{x^3} $
where k is a constant.
Or I may be wrong? If w varies jointly it could be $\displaystyle w = k \times \frac{z^2 \pm \sqrt{y}}{x^3} $