There are 10 class reunions. If two people shake hands once when they meet each other, how many times will they shake hands in total?
有10个同学聚会，如果两人见面互相握一次手，一共要握多少次手．
<gadget id="calculator">10 - 1</gadget>
<output>9</output>

<gadget id="calculator">10 / 2</gadget>
<output>5</output>

<gadget id="calculator">9 * 5</gadget>
<output>45</output>

<result>45</result>