There are 6 good friends at a party, and each of them shakes hands once, how many times should they shake hands in total?
有6个好朋友聚会，他们每两人握一次手，一共要握多少次手．
<gadget id="calculator">6 - 1</gadget>
<output>5</output>

<gadget id="calculator">5 / 2</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">6 * (5/2)</gadget>
<output>15</output>

<result>15</result>