A remote-control car moves across a playground from the point (-1, 4) to the point (11, -1), in…

Step 1. Displacement. $\Delta\vec{r} = (11 - (-1))\hat{i} + (-1 - 4)\hat{j} = (12\hat{i} - 5\hat{j})\ \text{m}$. Its size is $\sqrt{(12\ \text{m})^2 + (5\ \text{m})^2} = 13\ \text{m}$.

Step 2. Average velocity. $\dfrac{13\ \text{m}}{2.6\ \text{s}} = 5.0\ \text{m/s}$, along $12\hat{i} - 5\hat{j}$. As a vector, $\vec{v}_{\text{av}} = (4.6\hat{i} - 1.9\hat{j})\ \text{m/s}$.

Step 3. Average speed. $\dfrac{16\ \text{m}}{2.6\ \text{s}} = 6.15\ \text{m/s}$.