In a theater, there are 20 seats in the first row, and each subsequent row has 2 more seats than the previous row, making a total of 25 rows. How many seats are there in this theater?
一个剧院，第一排有20个座位，以后每排总比前一排多2个座位，一共是25排．这个剧院共有多少个座位？
<gadget id="calculator">25 - 1</gadget>
<output>24</output>

<gadget id="calculator">24 * 2</gadget>
<output>48</output>

<gadget id="calculator">20 + 48</gadget>
<output>68</output>

<gadget id="calculator">20 + 68</gadget>
<output>88</output>

<gadget id="calculator">25 / 2</gadget>
<output>25/2 = around 12.5</output>

<gadget id="calculator">88 * (25/2)</gadget>
<output>1_100</output>

<result>1_100</result>