A project can be completed in 4 days by A alone, and 5 days by B alone. What percentage of B's work efficiency is A's?
一项工程，甲单独做要4天完成，乙单独做要5天完成，乙的工作效率是甲的百分之几？
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(1/5) / (1/4)</gadget>
<output>4/5 = around 0.8</output>

<result>4/5 = around 0.8</result>