At a farewell party, 10 students shook hands to say goodbye, every two people shook hands once, how many times did they shake hands in total?
在一次欢送会上，10名同学握手告别，每两人握一次手，一共握了多少次手．
<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>