It takes A 4 days and B 5 days to complete the same job alone. B's work efficiency is the number of A's work efficiency.
单独完成同一件工作，甲要4天，乙要5天．乙的工作效率是甲的工作效率的多少．
<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>