剧场有多少座位：一个剧场设置了20 排座位，第一排有38 个座位，往后每一排都比前一排多2 个座位，这个剧场一共设置了多少个座位？

数学题解答：先算出最后一排座位有多少个？38+19×2＝76（个）。

然后可以按照梯形公式来计算座位总数，对应关系是：上底38，下底76，高20。

算式：（38+76）×20÷2＝1140（个）

推荐阅读：
New Report Discovers Disconnect Between Retailers And Social Med　 Counting the Prime Arrangements　 The Minimum Absolute Difference Algorithm of an Array　 Implement the Depth First Search Algorithm in Graph using Simple　 Beginner’s Introduction to PHP Memcached　 Using the Regular Expression to Replace External Links in WordPr　 5 Smart Guides In Taking The Best Hosting Provider　 Checking Subtree of Another Tree using Preorder Traversal or Rec　 How to Optimize WordPress Website for Speed?　 How to Compute the Day of the Week using C++?