几道GRE数学题

题目

几道GRE数学题
1.In a series of races,10 toys cars are raced,2 cars at a time.If
each car must race each of the other cars exactly twice,how many races must be held?
2.The daily rate for a hotel room that sleeps 4 people is $39 for one person
and x dollars for each additional person.If 3 people take the room for one day
and each pays $21 for the room,what is the value of
3.What fraction of the positive intergers that are multiples of 30 and are less than or equal to 360 are multiples of 12?
答案为1/2

答案

第一个题是排列组合的题,是说十辆车比赛,每次两辆车一起比赛,问如果每辆车需要和其他的每辆车比赛两次,需要举行多少次比赛.可以先考虑每辆车和其他的车各比赛一次,也就是10*9/2,在乘以2就是比赛两次的总场数啦~（组...