A manuscript is planned to be typed in 30 days, but (2/5) of the manuscript is actually completed in 8 days. How many days can it be completed in advance? (use three methods that you think are simple to answer)
一份稿件，计划30天打完，实际8天就完成这份稿件的(2/5)，照这样可以提前几天完成？(用三种你认为简捷的方法解答)
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(2/5) / 8</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">1 / (1/20)</gadget>
<output>20</output>

<gadget id="calculator">30 - 20</gadget>
<output>10</output>

<result>10</result>