There are 7 people participating in a table tennis match. If there is a match between 2 players, how many games will be played in total?
有7人参加乒乓球比赛，如果每2个人之间比赛一场，一共要赛多少场．
<gadget id="calculator">7 - 1</gadget>
<output>6</output>

<gadget id="calculator">6 / 2</gadget>
<output>3</output>

<gadget id="calculator">7 * 3</gadget>
<output>21</output>

<result>21</result>