On the "June 1st" festival, a total of 20 students from Hongxing Primary School signed up to participate in the "table tennis" competition, and were evenly divided into two groups, A and B. If every two students in each group played a game, how many games would there be in total?
"六一"节，红星小学共有20名同学报名参加"乒乓球"比赛，被平均分为A、B两组，如果每小组中每两名同学都进行一场比赛，一共要比赛多少场．
<gadget id="calculator">10 - 1</gadget>
<output>9</output>

<gadget id="calculator">9 / 2</gadget>
<output>9/2 = around 4.5</output>

<gadget id="calculator">10 * (9/2) * 2</gadget>
<output>90</output>

<result>90</result>