10 teams play a single round-robin game (one game for every two team sites), how many games will there be in total?
10支球队进行单循环比赛(每两个队部进行一场比赛)，一共要赛多少场．
<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)</gadget>
<output>45</output>

<result>45</result>