A pile of coal, the factory originally planned to burn 15 tons per day for 60 days, but actually saved 20% of the original plan every day. How many days did this batch of coal actually burn?
一堆煤，工厂原计划烧60天，每天烧15吨，实际每天比原计划节约20%，这批煤实际烧了多少天？
<gadget id="calculator">60 * 15</gadget>
<output>900</output>

<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">15 * (4/5)</gadget>
<output>12</output>

<gadget id="calculator">900 / 12</gadget>
<output>75</output>

<result>75</result>