There are 7 classes in a school participating in a basketball game. If there is a game between every two classes, how many games will there be in total?
某学校有7个班级参加篮球赛，如果每两个班级之间都进行一场比赛，一共要赛多少场．
<gadget id="calculator">7 - 1</gadget>
<output>6</output>

<gadget id="calculator">6 / 2</gadget>
<output>3</output>

<gadget id="calculator">7 * 3</gadget>
<output>21</output>

<result>21</result>