There are 7 classes in the third grade, and they are going to hold a tug-of-war competition, and there will be a competition between every two classes. How many games will they play in total?
三年级有7个班，准备举行拔河比赛，每2个班之间都进行一场比赛．他们一共要进行几场比赛？
<gadget id="calculator">7 - 1</gadget>
<output>6</output>

<gadget id="calculator">7 / 2</gadget>
<output>7/2 = around 3.5</output>

<gadget id="calculator">6 * (7/2)</gadget>
<output>21</output>

<result>21</result>