Seven classes in the sixth grade have a friendly basketball match, and every two classes have to play one game. How many games will there be in total?
六年级7个班进行篮球友谊赛，每两个班都要赛一场，一共要进行多少场比赛．
<gadget id="calculator">7 - 1</gadget>
<output>6</output>

<gadget id="calculator">7 / 2</gadget>
<output>7/2 = around 3.5</output>

<gadget id="calculator">6 * (7/2)</gadget>
<output>21</output>

<result>21</result>