[求助]再问几道prep的数学

玻璃胶带

1.The cost of each adult's ticket for a certain concert was $30, and the cost of each child's ticket for the concert was $24. If Hannah purchased tickets for this concert, what was the average(arithmetic mean) cost per ticket?

(1) Hannah purchased twice as many children's tickets as adults' tickets.
(2) Hannah purchased 4 children's tickets.

答案是a 不明白。。。为什么2不能推出来呢?

2.If n is a positive integer and r is the remainder when n^2-1 is divided by 8, what is the value of r?

(1) n is odd
(2) n is not divisible by 8

答案還是a。为什么n是奇数,就能推呢?我算出来n=3,5,7,9....疑惑???

3.The symbol represents one of the four arithmetic operations: addition, subtraction, multiplication, and division. Is (5&6)&2=5&(6&2)?

(1)  5&6=6&5
(2)  2&0=2

答案是a  第一个条件说明此符号满足交换律?

玻璃胶带

自己顶一下,有没有人回答我一下啊?

谢谢拉

shiverson

1.可能算是个trick吧，只说了买几个小孩儿票。不过我也觉得这么说不太好，但我想他要想表达一共买了几个肯定会说only或者total这类词吧。

2.n是奇数则n^2-1=(n+1)(n-1)。n=奇数说明括号里面两个都是偶数。相邻的两个偶数里，肯定有一个能被4整除对吧，所以它就能被8整除了啊，r=0

3.5※6=6※5说明这个※不是加就是乘，带进去不影响所求的计算结果啊，所以A...

玻璃胶带

以下是引用shiverson在2008-7-8 22:53:00的发言：

1.可能算是个trick吧，只说了买几个小孩儿票。不过我也觉得这么说不太好，但我想他要想表达一共买了几个肯定会说only或者total这类词吧。

2.n是奇数则n^2-1=(n+1)(n-1)。n=奇数说明括号里面两个都是偶数。相邻的两个偶数里，肯定有一个能被4整除对吧，所以它就能被8整除了啊，r=0

3.5※6=6※5说明这个※不是加就是乘，带进去不影响所求的计算结果啊，所以A...

哦! 明白拉! 谢谢shiverson!