The factory has to process 1,200 parts, and it was planned to be completed in 20 days, but 20% was actually completed in 3 days. According to this calculation, how many days can the task be completed in advance?
工厂要加工1200个零件，计划20天完成，实际3天就完成了20%，照这样计算，可提前几天完成任务？
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

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

<gadget id="calculator">3 * 5</gadget>
<output>15</output>

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

<result>5</result>