When 5 children met each other, how many times did they shake hands in total?
5个小朋友见了面，每两人都要握一次后，一共握了多少次手．
<gadget id="calculator">5 - 1</gadget>
<output>4</output>

<gadget id="calculator">4 / 2</gadget>
<output>2</output>

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

<result>10</result>