To express a number as a percentage of another, divide and multiply by 100.<br><br>
&bull; Percentage = \(\frac{4}{20} \times 100\%\)<br>
&bull; \(\frac{4}{20} = \frac{1}{5} = 0.2\)<br>
&bull; \(0.2 \times 100\% = 20\%\)<br><br>
Final Answer: 20