Processing a batch of parts, originally planned to process 80 pieces per day, just completed the task on schedule. Due to the improvement of production technology, 100 parts are actually processed every day. This not only completes the processing task 4 days ahead of schedule, but also processes 100 more parts. How many parts were originally planned to be processed?
加工一批零件，原计划每天加工80个，正好按期完成任务．由于改进生产技术，实际每天加工100个，这样不仅提前4天完成加工任务，而且还多加工了100个零件，原计划加工零件多少个？
<gadget id="calculator">100 * 4</gadget>
<output>400</output>

<gadget id="calculator">400 + 100</gadget>
<output>500</output>

<gadget id="calculator">100 - 80</gadget>
<output>20</output>

<gadget id="calculator">500 / 20</gadget>
<output>25</output>

<gadget id="calculator">25 * 80</gadget>
<output>2_000</output>

<result>2_000</result>