A bag of flour is used for the first time (1/5), and 25 kilograms are used for the second time, leaving exactly 15 kilograms. How many kilograms are there in this bag of flour?
一袋面粉，第一次用去(1/5)，第二次用去25千克，刚好剩下15千克，这袋面粉共有多少千克？
<gadget id="calculator">25 + 15</gadget>
<output>40</output>

<gadget id="calculator">1 / 5</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>