When 8 old friends got together, each of them shook hands once, how many times did they shake hands in total?
8位老朋友聚会，每两人之间都握了一次手，一共握了多少次手．
<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>