A batch of coal was shipped from a power plant, and it was originally planned to burn 15 tons per day, which would take 80 days to burn out. The actual saving is 20% than the original plan every day. How many days did it actually burn?
某发电厂运来一批煤，原计划每天烧15吨，80天烧完．实际每天比原计划节约了20%，实际烧了多少天？
<gadget id="calculator">15 * 80</gadget>
<output>1_200</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">1_200 / 12</gadget>
<output>100</output>

<result>100</result>