There are 6 classes in Yucai Primary School holding basketball games. If there is a game between every two classes, how many games will there be in total?
育才小学有6个班举行篮球比赛，如果每两个班之间都要进行一场比赛，一共要比赛多少场．
<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>