There is a batch of parts, repaired on the first day (2/5), and repaired on the second day (1/5), there are still 20 parts left, how many parts are there in this batch?
有一批零件，第一天修了(2/5)，第二天修了(1/5)，还剩20个，这批零件有多少个？
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

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

<gadget id="calculator">1 - (2/5) - (1/5)</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">20 / (2/5)</gadget>
<output>50</output>

<result>50</result>