Xiao Hua's 4 friends come to his house to play with him, if each of them shakes hands once, how many times will they shake hands in total?
小华的4位朋友来他家和他一起玩，如果他们每两个人都要握一次手，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>