A total of 10 athletes participate in a certain sports competition. If every two people shake hands once, how many times do they shake hands in total?
共有10名运动员参加某场体育比赛，如果每两人握一次手，一共握了多少次手．
<gadget id="calculator">10 - 1</gadget>
<output>9</output>

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

<gadget id="calculator">9 * 5</gadget>
<output>45</output>

<result>45</result>