There are 210 kilograms in a barrel of oil, and the remaining 40% is used, how many kilograms are left.
一桶油有210千克，用去的是剩下的40%，剩下多少千克．
<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 + (2/5)</gadget>
<output>7/5 = around 1.4</output>

<gadget id="calculator">210 / (7/5)</gadget>
<output>150</output>

<result>150</result>