9 students play table tennis, every two students have to play one game, how many games will be played in total.
9位同学打乒乓球，每两个同学都要比赛一场，一共要进行多少场比赛．
<gadget id="calculator">9 - 1</gadget>
<output>8</output>

<gadget id="calculator">9 / 2</gadget>
<output>9/2 = around 4.5</output>

<gadget id="calculator">8 * (9/2)</gadget>
<output>36</output>

<result>36</result>