Every two people make a phone call, so how many times are there 5 people in total?
每两个人通一次电话，所以5个人一共通多少次次电话．
<gadget id="calculator">5 - 1</gadget>
<output>4</output>

<gadget id="calculator">5 / 2</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">4 * (5/2)</gadget>
<output>10</output>

<result>10</result>