Master Wang processes a batch of parts, planning to process 20 per day, but actually processes 5 more per day, so that it is completed 4 days ahead of schedule. How many parts are there in this batch?
王师傅加工一批零件，计划每天20个，实际每天多加工5个，这样提前4天完成，这批零件共有多少个？
<gadget id="calculator">20 + 5</gadget>
<output>25</output>

<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">25 * (4/5) * 25 * (4/5)</gadget>
<output>400</output>

<result>400</result>