There are 6 students playing table tennis. Every two students play a game. How many games are there in total?
有6名同学进行乒乓球比赛，每两名同学之间都进行一场比赛，共比赛多少场．
<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>