SAT数学,有关排列组合in a certain soccere league, each of the five teams plays every other team in the league exactly three times each season. How many games are played in total in one season?答案是30.为什么?
问题描述：
SAT数学,有关排列组合
in a certain soccere league, each of the five teams plays every other team in the league exactly three times each season. How many games are played in total in one season?
答案是30.为什么?
答
先算一只球队一个赛季的场数，不会打排列组合的符号囧
就简单字符说明吧，好在只有5个队
A B C D E
A-B,A-C,A-D,A-E
B-C,B-D,B-E
C-D,C-E
D-E
这是10场
3倍30场。。。
答
用最普通的方法想,每个队和其他4个队各比一次,两队之间又是重复的,就是（5*4）/2次,再乘3就是总次数~
其实用公式很简单,不过我也忘得差不多了,也不知道那符号怎么打出来……总之祝考试成功~