There is a pile of coal in the school cafeteria. (3/10) tons were used in the first week, (7/20) tons were used in the second week, and (1/5) of this pile of coal was used in two weeks. The pile of coal has a total of How many tons?
学校食堂有一堆煤，第一周用了(3/10)吨，第二周用了(7/20)吨，两周正好用了这堆煤的(1/5)，这堆煤一共有多少吨？
<gadget id="calculator">3 / 10</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">7 / 20</gadget>
<output>7/20 = around 0.35</output>

<gadget id="calculator">(3/10) + (7/20)</gadget>
<output>13/20 = around 0.65</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(13/20) / (1/5)</gadget>
<output>13/4 = around 3.25</output>

<result>13/4 = around 3.25</result>