During the New Year's Day, among the 5 basketball teams A, B, C, D, and E, every 2 teams played a game, how many games did they play in total?
元旦期间，A、B、C、D、E这5支篮球队中，每2支球队都进行一场球赛，他们一共进行了多少场球赛．
<gadget id="calculator">5 - 1</gadget>
<output>4</output>

<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">5 * 2</gadget>
<output>10</output>

<result>10</result>