A pile of coal, originally planned to burn 1.2 tons per day, can be burned for 60 days. After the technology is improved, the pile will be burned for 30 days longer. How many tons of coal can be saved on average?
一堆煤，原计划每天烧1.2吨，可以烧60天，改进技术后结果这堆多烧30天，平均节省煤多少吨？
<gadget id="calculator">60 + 30</gadget>
<output>90</output>

<gadget id="calculator">60 / 90</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">1.2 * (2/3)</gadget>
<output>0.8</output>

<gadget id="calculator">1.2 - 0.8</gadget>
<output>0.4</output>

<result>0.4</result>