The mathematical representation of a machine's efficiency is commonly expressed as:
\[ \text{Efficiency} = \frac{E_o}{E_i} \times 100 \]
Where \( E_o \) represents the useful output energy and \( E_i \) represents the input energy.
Thus, the correct response from your options would be:
Efficiency = \( \frac{E_o}{E_i} \times 100 \) (Efficiency = cap e o over cap e i 100).