[求助]请教prep ds1-38

小午123

If r and s are positive integers, is  an integer?

 

(1)  Every factor of s is also a factor of r.

 

(2)  Every prime factor of s is also a prime factor of r.

答案是Ａ，可是我不太明白（２）为什么不对呀？谢谢！！

iamsean

以下是引用小午123在2008-6-11 23:00:00的发言：

If r and s are positive integers, is  an integer?

(1)  Every factor of s is also a factor of r.

(2)  Every prime factor of s is also a prime factor of r.

答案是Ａ，可是我不太明白（２）为什么不对呀？谢谢！！

题目貌似不完整啊

fanstar1987

数字120和数字30....

小午123

啊不好意思,原题粘过来没有了没注意到,重发一下:

If r and s are positive integers, is r/s  an integer?

  (1)  Every factor of s is also a factor of r.

  (2)  Every prime factor of s is also a prime factor of r.

答案是Ａ，可是我不太明白（２）为什么不对呀？谢谢！！

fanstar1987

那么就是30和120？

比出来=1/4

30:1 2 3 5

120:1 2 3 5   4

小午123

啊啊啊,明白了!!想了好久啊这题，谢谢fanstar!!!!

lyricsea

条件一说明s是r的一个factor，所以r/s肯定是整数。

条件二不充分，举个例子设s＝12，则质因数是1.2.3，设r＝6，质因数是1.2.3。但是6/12不是整数吧。

呵呵。

小午123

恩恩,讲得好清楚啊！谢谢！！