A cement factory purchased a pile of coal. It was originally planned to burn 12 tons per day, and it could be burned for 15 days. The actual daily coal consumption was 25% lower than the original plan. How many days did the pile of coal actually burn? (Answer with proportional knowledge)
水泥厂购进一堆煤，原计划每天烧12吨，可以烧15天，实际每天烧煤比原计划节约25%，这堆煤实际烧了多少天？(用比例知识解答)
<gadget id="calculator">12 * 15</gadget>
<output>180</output>

<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">12 * (1/4)</gadget>
<output>3</output>

<gadget id="calculator">12 - 3</gadget>
<output>9</output>

<gadget id="calculator">180 / 9</gadget>
<output>20</output>

<result>20</result>