5 students play table tennis, and every two players play one game, how many games will they play in total?
5名同学打乒乓球，每两人打一场，共要打多少场．
<gadget id="calculator">5 - 1</gadget>
<output>4</output>

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

<gadget id="calculator">4 * (5/2)</gadget>
<output>10</output>

<result>10</result>