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：
The Python Function to Retrieve the Producer Reward for Witness　 Function to Compute the Average Salary Excluding the Minimum and　 Efficient Algorithms to Compute The kth Factor of a Natural Numb　 Can We Make Arithmetic Progression From Sequence of Numbers?　 How to SSH to Remote Host using the Priviate/Public Keys Authent　 How do you Test Getter and Setter Interface in Java using Mockit　 Using Java’s Big Integer to Compute the Large Sum of One-h　 IoT Security: Real Problems and Solutions　 Set Up Website Health Checks (Canaries) using CloudFlare　 Deep Clone N-ary Tree using Hash Map + Recursive Depth First Sea