Track radius circumference

The runner circled the track three times. If he went around it once more, he would run one kilometer. What is the radius of the treadmill?

Final Answer:

r =  39.79 m

Step-by-step explanation:

$$\begin{gathered} (3+1)o=1km \\ 4o=1000m \\ 4\cdot 2\pi \cdot r=1000 \\ r=\frac{1000}{4\cdot 2\pi }=\frac{1000}{4\cdot 2\cdot 3.1416}=39.79\text{m} \end{gathered}$$

Try another example