When two people meet, they shake hands once. According to this rule, how many times do 10 people shake hands in total?
两个人见面要握一次手．照这样规定，10个人见面共握手多少次．
<gadget id="calculator">10 - 1</gadget>
<output>9</output>

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

<gadget id="calculator">10 * (9/2)</gadget>
<output>45</output>

<result>45</result>