On May 1, 2010, the 41st World Expo opened in Shanghai. As of June 6, the highest single-day visitor flow of the World Expo was about 520,000 person-times, 120,000 person-times more than twice the number of visitors on the day of the opening ceremony. How many people visited the Expo on the day of the opening ceremony? (Solution of column equation)
2010年5月1日第41届世博会在上海开幕．截至6月6日，世博会单日最高客流量约是52万人次，比开幕式当日入园人次的2倍还多12万人次．世博会开幕式当天有多少万人次进园参观？(列方程解)
<gadget id="calculator">52 - 12</gadget>
<output>40</output>

<gadget id="calculator">40 / 2</gadget>
<output>20</output>

<result>20</result>