Let $k$ be a field. If $A \in k^{m \times n}$ and $B \in k^{n \times p}$, then $\operatorname{rank}(AB) \le \min\{\operatorname{rank}(A),\operatorname{rank}(B)\}$. If $A,B \in k^{m \times n}$, then $\operatorname{rank}(A+B) \le \operatorname{rank}(A)+\operatorname{rank}(B)$.