A pile of coal is planned to burn 0.5 tons per day, which can be burned for 40 days. The actual amount of coal burned every day is only 4/5 of the original plan. How many days can this pile of coal actually be burned?
一堆煤，计划每天烧0.5吨，可以烧40天．实际每天烧的煤只有原计划的(4/5)，这堆煤实际可以烧多少天？
<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">0.5 * (4/5)</gadget>
<output>0.4</output>

<gadget id="calculator">40 / 0.4</gadget>
<output>100</output>

<gadget id="calculator">0.5 * 100</gadget>
<output>50</output>

<result>50</result>