2011 AMC 12B Problem 9

Two real numbers are selected independently and at random from the interval [-20,10]. What is the probability that the product of those numbers is greater than zero?

\textbf{(A)}\ \frac{1}{9} \qquad \textbf{(B)}\ \frac{1}{3} \qquad \textbf{(C)}\ \frac{4}{9} \qquad \textbf{(D)}\ \frac{5}{9} \qquad \textbf{(E)}\ \frac{2}{3}

Full credit goes to MAA for authoring these problems. These problems were taken on the AOPS website.