To calculate percent efficiency using the formula provided:
\[ \text{Percent Efficiency} = \left( \frac{\text{Actual MA}}{\text{Ideal MA}} \right) \times 100 \]
Substituting the given values:
\[ \text{Percent Efficiency} = \left( \frac{10 , \text{J}}{40 , \text{J}} \right) \times 100 \] \[ \text{Percent Efficiency} = \left( 0.25 \right) \times 100 \] \[ \text{Percent Efficiency} = 25% \]
Thus, the percent efficiency is 25%.