The school organizes table tennis competitions. Xiao Ding Ding's team has 6 players. There is a comparison between every 2 people in the group. How many games does Xiao Ding Ding's group have to play?
学校组织乒乓球比较，小丁丁所在的小组共有6名选手，小组中每2人之间都要进行一场比较，小丁丁所在的小组共要进行多少比赛．
<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>