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183. 17831-!-item-!-187;#058&011633 If mis a positive odd integer between 2 and 30, then m is divisible by how manydifferent positive prime numbers? (1)m is not divisible by 3. (2)m is not divisible by 5. PREP 解答给的是A，其实是C
下面是原始解答：
【答案】A 【思路】 2<m<30
{3,5,7,9,11,13,15,17,19,21,23,25,27,29}
(1) m excludes {3,6,9,12,15,18,21,24,27}={5,7,11,13,17,19,23,25,29} 全部只可以被自己和1除 很明显这里的25有三个
(2) m excludes {5,10,15,20,25}={3,7,9,11,13,17,19,21,23,27,29} 21除了自己和1還可以被7除
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发表于 2017-4-21 09:46:08
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