There are 6 people in the first group, if every two people make a phone call. How many phone calls did you have to make in total?
第一小组有6个人，如果每两人之间通一次电话．一共要通多少次电话．
<gadget id="calculator">6 - 1</gadget>
<output>5</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

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

<gadget id="calculator">30 / 2</gadget>
<output>15</output>

<result>15</result>