The school held a badminton trial, and each contestant had to play a game against all other players. If there are 20 contestants, how many trials will be conducted in total?
学校进行羽毛球选拔赛，每个参赛选手都要和其他所有选手赛一场．若有20人参赛，那么一共要进行多少场选拔赛．
<gadget id="calculator">20 - 1</gadget>
<output>19</output>

<gadget id="calculator">19 / 2</gadget>
<output>19/2 = around 9.5</output>

<gadget id="calculator">20 * (19/2)</gadget>
<output>190</output>

<result>190</result>