40% of a bag of flour is used up, and the rest is 20 kg more than what was used. How much does the bag of flour weigh?
一袋面粉用去40%，剩下的比用去的多20千克，这袋面粉原来重多少千克？
<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">(3/5) - (2/5)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">20 / (1/5)</gadget>
<output>100</output>

<result>100</result>