A pile of gravel, 20% of the total amount was transported for the first time, and 105 tons were transported for the second time, leaving (11/20) of the total amount. How many tons are there in this pile of gravel?
一堆砂石，第一次运走了总数的20%，第二次运走了105吨后，剩下总数的(11/20)，这堆砂石共有多少吨？
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">11 / 20</gadget>
<output>11/20 = around 0.55</output>

<gadget id="calculator">1 - (1/5) - (11/20)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">105 / (1/4)</gadget>
<output>420</output>

<result>420</result>