jmc

First, we factor the equation as $x(x^2+3x-10)=0$. So, one solution is $x=0$ and the other two solutions are the solutions to $x^2+3x-10=0$. We could either factor the quadratic, or note that the sum of the solutions to this quadratic is $-(3/1)=-3$, so the mean of the three solutions to the original equation is $-3/3=\boxed{-1}$.