Four teams play football, and every two teams have to play one game. How many games are there in total?
四个球队踢足球，每两个球队都要比赛1场，一共要比赛多少场．
<gadget id="calculator">4 - 1</gadget>
<output>3</output>

<gadget id="calculator">3 / 2</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">4 * (3/2)</gadget>
<output>6</output>

<result>6</result>