9 students are playing table tennis. If every two students play a game, how many games will there be in total?
9名同学进行乒乓球比赛，如果每两名同学之间都进行一场比赛，一共要比赛多少场．
<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>