Teacher Zhang and 9 people present at the meeting, any two of them shake hands once, how many times in total.
张老师与到会的9人，任意两人之间都握一次手，一共握多少次手．
<gadget id="calculator">9 - 1</gadget>
<output>8</output>

<gadget id="calculator">9 / 2</gadget>
<output>9/2 = around 4.5</output>

<gadget id="calculator">8 * (9/2)</gadget>
<output>36</output>

<result>36</result>