Teacher Wang and 5 athletes, if every 2 people shake hands once, how many times did they shake hands in total?
王老师与5名运动员，如果每2人握一次手，一共握了多少次手．
<gadget id="calculator">5 + 1</gadget>
<output>6</output>

<gadget id="calculator">1 - 1</gadget>
<output>0</output>

<gadget id="calculator">5 + 0</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>