TeX source:
\begin{array}{rclcr}27\;\text{Affen}&\widehat{=}& 100\,\% \cr \cr 1\;\text{Affe}&\widehat{=}& \dfrac{100\,\%}{27} \cr \cr 15\;\text{Affen}&\widehat{=}& \dfrac{15\cdot 100\,\%}{27} &\approx& 55{,}56\,\% \end{array}