A project, A alone takes 20 minutes, and B alone takes 15 minutes, how much lower is A's work efficiency than B
一项工程，甲单独做要20分钟，乙单独做要15分钟，甲的工作效率比乙低多少
<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(1/15) - (1/20)</gadget>
<output>1/60 = around 0.016667</output>

<gadget id="calculator">(1/60) / (1/15)</gadget>
<output>1/4 = around 0.25</output>

<result>1/4 = around 0.25</result>