Teacher Li and 8 of his classmates have a party. If every 2 people shake hands once, how many times will they shake hands in total?
李老师与他的8个同学聚会，如果每2人之间都要握一次手，一共要握手多少次．
<gadget id="calculator">8 - 1</gadget>
<output>7</output>

<gadget id="calculator">8 / 2</gadget>
<output>4</output>

<gadget id="calculator">7 * 4</gadget>
<output>28</output>

<result>28</result>