[求助]prep里的两道数学题

kirstenrl87

DS: 1. If d is a positive integer and f is the product of the first 30 positive integers, what is the value of d?

(1) 10^d is a factor of f     (2) d>6

答案选C，这是怎么算出来的呢？

2. 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

这道答案选A，可我觉得要选C啊，哪位NN能不能来解答一下~

fiona8718

同问

andygogogo

    for No.2 , just list the numbers and you will understand


        

2. 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

    
        

3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29

    
        

 

    
        

(1). 5, 7, 11, 13, 17, 19, 23, 25, 29 (identical)

            

    (2). 3, 5, 7, 11, 13, 17, 19, 21, 23, 27, 29 (various)
                

[此贴子已经被作者于2008-10-15 13:01:14编辑过]

wenshan1117

(1)應該有25? 而25是單一的沒錯 因為25只被一個質數5整除 (2)應該沒有5吧?? 而且27應該是只被單一的質數3整除 只有21才是被兩個質數3和7整除

[此贴子已经被作者于2008-10-15 8:54:13编辑过]

kirstenrl87

但如果是（1）的话，m为什么不可以等于25呢，这样一来（1）就不能单独成立了呀~

willwang0110

以下是引用kirstenrl87在2008-10-15 8:50:00的发言：
但如果是（1）的话，m为什么不可以等于25呢，这样一来（1）就不能单独成立了呀~

这道题目最艰险的地方就在于25也是可以的 只有一个质因数5阿~

fiona8718

啊...明白了.可第一题为什么呢?

andygogogo

不好意思,25打漏啦, 哈哈