In June, the factory actually produced 600 parts per day and completed the task in 20 days. It planned to produce 500 parts per day. How many days earlier than planned was the task completed?
工厂六月份实际每天生产600个零件，20天完成任务，计划每天生产500个零件，比计划提前多少天完成任务？
<gadget id="calculator">20 / 500</gadget>
<output>1/25 = around 0.04</output>

<gadget id="calculator">600 * (1/25)</gadget>
<output>24</output>

<gadget id="calculator">24 - 20</gadget>
<output>4</output>

<result>4</result>