There are 10 table tennis players in the school on "Six Day" Children's Day. If every two players have to play one game, how many games will it take?
"六一"儿童节学校有10名选手进行乒乓球比赛，如果每两个人都要赛一场一共需要赛多少场．
<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>