Seven classmates go to the teacher's house for a party. If every two people must shake hands once, how many times will they shake hands in total?
7个同学到老师家聚会，如果每两个人之间都必须握一次手，那么一共要握多少次手．
<gadget id="calculator">7 + 1</gadget>
<output>8</output>

<gadget id="calculator">7 / 2</gadget>
<output>7/2 = around 3.5</output>

<gadget id="calculator">8 * (7/2)</gadget>
<output>28</output>

<result>28</result>