There are 10 basketball teams holding a friendly basketball match, and each team plays exactly one game against the other teams. 3 points for a win; 0 points for a loss; 1 point for a draw. After the game, the total score of all teams is 120 points. So, how many games in the game ended in a draw.
有10支篮球队举行篮球友谊赛，每支球队都恰与其他球队各赛一场．胜一场得3分；负一场得0分；若为平局，各得1分．比赛结束后，所有球队的总得分为120分．那么，比赛中有多少场比赛结果是平局．
<gadget id="calculator">10 - 1</gadget>
<output>9</output>

<gadget id="calculator">9 / 2</gadget>
<output>9/2 = around 4.5</output>

<gadget id="calculator">3 * 10 * (9/2)</gadget>
<output>135</output>

<gadget id="calculator">135 - 120</gadget>
<output>15</output>

<gadget id="calculator">3 - 2</gadget>
<output>1</output>

<gadget id="calculator">15 / 1</gadget>
<output>15</output>

<result>15</result>