There are 10 classmates in a reunion, each of them should shake hands once, how many times should they shake hands in total?
10名同学聚会，每两人都要握一次手，一共要握多少次手．
<gadget id="calculator">10 - 1</gadget>
<output>9</output>

<gadget id="calculator">2 / 9</gadget>
<output>2/9 = around 0.222222</output>

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

<gadget id="calculator">90 / 2</gadget>
<output>45</output>

<result>45</result>