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求助prep数学题!!急!!谢谢!!

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楼主
发表于 2011-4-17 19:51:40 | 只看该作者 回帖奖励 |倒序浏览 |阅读模式
183.17831-!-item-!-187;#058&011633

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.

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沙发
发表于 2011-4-17 21:06:26 | 只看该作者
3,5,7,9,11,13,15,17,19,21,23,25,27,29

Note, the above has many prime numbers and multiples of 3 and/or 5.

But if both 1) and 2) are right, you only have prime numbers left.

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板凳
 楼主| 发表于 2011-4-17 21:08:26 | 只看该作者
thank you but the answer on prep is A ? Why?
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