20% of the total weight of a bag of flour was used in the first week, and 15kg was used in the second week, leaving 25kg. How much does the bag of flour weigh?
一袋面粉，第一周用了总质量的20%，第二周用了15kg，还剩25kg，这袋面粉重多少kg．
<gadget id="calculator">15 + 25</gadget>
<output>40</output>

<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">40 / (4/5)</gadget>
<output>50</output>

<result>50</result>