A pile of sand was used to build a house (2/5), exactly 4 tons were used. How many tons is this pile of sand?
一堆沙，盖房用去了(2/5)，正好用去了4吨．这堆沙共有多少吨？
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">4 / (2/5)</gadget>
<output>10</output>

<result>10</result>