To produce a batch of parts, worker A can complete it in (1/4) hour alone, and worker B can complete it in (1/5) hour alone. Worker A makes 20 fewer parts per hour than worker B. How many parts are there in this batch?
生产一批零件，甲工人独做(1/4)小时可以完成，乙工人独做(1/5)小时可以完成．甲工人每小时比乙工人少做20个零件，这批零件一共有多少个？
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

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

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 / (1/4)</gadget>
<output>4</output>

<gadget id="calculator">5 - 4</gadget>
<output>1</output>

<gadget id="calculator">20 / 1</gadget>
<output>20</output>

<result>20</result>