Aus Online Mathematik Brückenkurs 1

Because the wheel's circumference is

\displaystyle 2\pi\cdot\text{(radius)} = 2\pi\cdot 0\textrm{.}5\ \text{metres} = \pi\ \text{metres}

the wheel turns \displaystyle \pi metres on each revolution, and in 10 metres the wheel therefore turns

\displaystyle \frac{10\ \text{metres}}{\pi\ \text{metres}} = \frac{10}{\pi }\ \textrm{revolutions}\approx 3\textrm{.}2\ \textrm{revolutions.}