4 children talk on the phone, every 2 people make one call, how many calls in total.
4个小朋友通电话，每2人通一次话，一共通多少次话．
<gadget id="calculator">4 - 1</gadget>
<output>3</output>

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

<gadget id="calculator">4 * (3/2)</gadget>
<output>6</output>

<result>6</result>