1500 parts are processed, and 20% of them are completed in 3 days. According to this calculation, how many days are needed for the remaining tasks? (Solved by two methods, at least one is the proportional method)
加工1500个零件，3天就完成了20%，照这样计算，剩下的任务还需要多少天？(用两种方法解答，至少一种是比例法)
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

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

<gadget id="calculator">(1/5) / 3</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(4/5) / (1/15)</gadget>
<output>12</output>

<result>12</result>