## Algebra 2 (1st Edition)

The general equation for joint variation is: $z=axy$ where $a$ is some constant. Then plugging in the given values for $z,x,y$ we get: $24=a(4)(-3)=-12a\\a=-2$. Thus the model is: $z=-2xy$. Then plugging in $x=-2,y=5$: $z=-2(-2)(5)=20$