5 children are playing table tennis, and every 2 players will play one game, how many games will be played in total.
5个小朋友进行乒乓球比赛，每2人都要赛一场，一共要进行多少场比赛．
<gadget id="calculator">4 / 2</gadget>
<output>2</output>

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

<result>10</result>