7 children attend a party, every 2 children have to shake hands once, how many handshakes are needed in total.
7位小朋友参加一次聚会，每2位小朋友都要握一次手，一共要握多少次手．
<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>