这道prep答案错了吧，否则无法解释，请大家帮帮忙

hebeqiao

A certain list consists of several different integers. Is the product of all integers in the list positive?

1, The product of the greatest and smallest of the integers in the list is positive.

2, There are even number of integers in the list.

Answer is C. 但是结合1和2， 有可能数列中有0，则所有数的乘积为0。应该选E啊。

还有以下两道题请教大家思路：

If m is a positive odd integer between 2 and 30, then m is divisible by how many different positive prime numbers?

1, m is not divisible by 3

2, m is not divisible by 5

Answer is A, why???

If a<y<z<b, is y-a的绝对值<y-b的绝对值吗？

1, z-a的绝对值<z-b的绝对值

2, y-a的绝对值<z-b的绝对值

Answer is D, but why????

boston8899

1. can only be all positive or all negative;

2. all odd between 2 and 30, not prime number, can either be divided by 3 or 5; if not 3 and not prime, then it has to be 25, either way it can only be divided by one prime number

on the other hand,if not divided by 5, then 21=3*7, 9=3^2

3. |z-a|>|y-a| bu <|z-b|<|y-b|; |y-a|<|z-b|<|y-b|

hebeqiao

???

or yes, got it. Many thanks!!

[此贴子已经被作者于2008-1-16 9:07:08编辑过]

boston8899

did you see that m is between 2 and 30? 7 has one prime number. 3,5,7...etc. can only be divided by themselves. that counts for once.

hebeqiao

yes, you are right. Thank you so much!