9 students participate in a badminton match, if every 2 students play a match, how many games are needed in total?
9名同学参加羽毛球比赛，如果每2名同学之间分别进行一场比赛，共需比赛多少场？
<gadget id="calculator">9 - 1</gadget>
<output>8</output>

<gadget id="calculator">8 / 2</gadget>
<output>4</output>

<gadget id="calculator">9 * 4</gadget>
<output>36</output>

<result>36</result>