Matrices Practice Test

In network analysis, $A=\begin{pmatrix}0&1&1\1&0&0\1&0&0\end{pmatrix}$ is an adjacency matrix; what does $\det(A)$ indicate about invertibility?

In an input-output model, $A=\begin{pmatrix}0.2&0.1\0.3&0.2\end{pmatrix}$ and demand $\vec d=\begin{pmatrix}50\40\end{pmatrix}$; what is $A\vec d$?