In a party, 10 students shake hands, if every two people shake hands once, how many times will they shake hands in total?
在一次联欢会上，10名同学握手，若每两人之间握一次手，共握多少次手．
<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>