The ticket price of a park is: 30 yuan per person for ordinary tickets, and 30% off for group tickets (more than 30 people). A school organizes 40 students to visit the park, how much is the minimum cost to buy tickets.
某公园门票价格为：普通票30元/人，团体票(30人以上)打七折．某校组织40名同学游览公园，买门票最少需要多少元．
<gadget id="calculator">70 / 100</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">30 * 40 * (7/10)</gadget>
<output>840</output>

<result>840</result>