Teacher Li met 4 friends who hadn’t seen each other for many years at a party. They shook hands once each, and how many times did they shake hands in total?
李老师在一次聚会上遇见4个多年不见的好友，他们每两人握一次手，一共要握多少次手．
<gadget id="calculator">5 - 1</gadget>
<output>4</output>

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

<gadget id="calculator">4 * (5/2)</gadget>
<output>10</output>

<result>10</result>