If the runner ends where she started, then her total displacement is [tex]\Delta x=0\,\mathrm m[/tex], which means her average velocity will be
[tex]\bar v=\dfrac{\Delta x}{\Delta t}=\dfrac{0\,\mathrm m}{4.0\,\mathrm{min}\cdot\frac{60\,\mathrm s}{1\,\mathrm{min}}=0\,\dfrac{\mathrm m}{\mathrm s}[/tex]
The total distance she traversed, however, was [tex]\Delta d=800\,\mathrm m[/tex], which gives her an average speed of
[tex]\bar s=\dfrac{\Delta d}{\Delta t}=\dfrac{800\,\mathrm m}{4.0\,\mathrm{min}\cdot\frac{60\,\mathrm s}{1\,\mathrm{min}}=3.3\,\dfrac{\mathrm m}{\mathrm s}[/tex]
