There are 5 players in a game, and every two players have to play one game, how many games will be held in total.
一次比赛有5位选手，每两人都要赛一场，一共要举行多少场比赛．
<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>