There is a pile of sand, after transporting 35% of the total amount, there are still 13 tons left. How many tons is this pile of sand?
有一堆沙子，运走了总数的35%后，还剩13吨，这堆沙子原来有多少吨？
<gadget id="calculator">35 / 100</gadget>
<output>7/20 = around 0.35</output>

<gadget id="calculator">1 - (7/20)</gadget>
<output>13/20 = around 0.65</output>

<gadget id="calculator">13 / (13/20)</gadget>
<output>20</output>

<result>20</result>