6 students play table tennis in a round-robin game, how many games will they play in total?
6个学生打乒乓球单循环比赛，一共要打多少场比赛．
<gadget id="calculator">6 - 1</gadget>
<output>5</output>

<gadget id="calculator">5 / 2</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">6 * (5/2)</gadget>
<output>15</output>

<result>15</result>