A workshop plans to process a batch of parts. If it processes 40 parts per day, it will be completed 1 day later than planned. If it processes 50 parts per day, it will be completed 2 days earlier than planned. How many parts are there in this batch?
某车间计划加工一批零件，如果每天加工40个零件，则比计划推迟1天完成，如果每天加工50个零件，则比计划提前2天完成，这批零件共有多少个．
<gadget id="calculator">1 + 2</gadget>
<output>3</output>

<gadget id="calculator">1 / 40</gadget>
<output>1/40 = around 0.025</output>

<gadget id="calculator">1 / 50</gadget>
<output>1/50 = around 0.02</output>

<gadget id="calculator">(1/40) - (1/50)</gadget>
<output>1/200 = around 0.005</output>

<gadget id="calculator">3 / (1/200)</gadget>
<output>600</output>

<result>600</result>