Voorbeeld 3

Er is gegeven dat $u_{1,1}=5$, $u_{1,2}=3$, $u_{1,1}=6$ en $u_{1,1}=8$.

Dan

$$\begin{align} \sum_{k=1}^2 \sum_{j=1}^2 u_{k,j} & = \sum_{k=1}^2 (u_{k,1}+u_{k,2})\\ & = (u_{1,1}+u_{1,2})+(u_{2,1}+u_{2,2})\\ & = 5+3+6+8\\ & =22, \end{align}$$

maar ook

$$\begin{align} \sum_{j=1}^2 \sum_{k=1}^2 u_{k,j} & = \sum_{j=1}^2 (u_{1,j}+u_{2,j})\\ & = (u_{1,1}+u_{2,1})+(u_{1,2}+u_{2,2})\\ & = 5+6+3+8\\ & =22. \end{align}$$