If every two children make one phone call, how many calls will 3 children make in total?
每两个小朋友通一次电话，3个小朋友共通多少次电话．
<gadget id="calculator">3 - 1</gadget>
<output>2</output>

<gadget id="calculator">3 / 2</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">2 * (3/2)</gadget>
<output>3</output>

<result>3</result>