The five classes of the sixth grade have a football match, and there is a match between every two classes. How many games are played in the whole year?
六年级五个班进行足球比赛，每2个班之间都要进行一场比赛，全年级共赛多少场
<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>