One project was completed in 15 days, 5 days more than the original plan, and the work efficiency was reduced ((())/(())).
一件工程15天完成，比原计划多用了5天，工作效率降低了((())/(()))．
<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">15 + 5</gadget>
<output>20</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>