10 good friends, every two people shake hands once, how many times do you shake hands in total?
10个好朋友，每两人握手1次，大家一共要握多少次手．
<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>