Our school carries out the "Welcome New Year's Day" tug-of-war competition. There are 6 classes in the fourth grade, and there will be a game between every two classes. How many games will be played in total.
我校开展"迎元旦"拔河比赛，四年级有6个班，每两个班之间都要比赛一场，一共要进行多少场比赛．
<gadget id="calculator">6 - 1</gadget>
<output>5</output>

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

<gadget id="calculator">5 * 3</gadget>
<output>15</output>

<result>15</result>