一道sat数学题how many integers greater than 20 and less than 30 a

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一道sat数学题
how many integers greater than 20 and less than 30 are each the product of exactly two different numbers,both of which are prime 答案是D=3 我算的是有21 22 23 29

题目是:大于20小于30的整数中,有多少个是两个不同质数的积
答案是:21=3*7,22=2*11,26=2*13,一共3个
楼主理解题目错了吧?23和29我不知道你是怎么得到的
再问：我当时考虑的是 1X23 1X29 这样考虑为什么不行
再答：因为题意中很明确,both of which are prime, prime的意思是质数,1明显不是质数,所以只有2*11,2*13,3*7,5*5,而另一个要求是two different numbers,所以5*5不符,所以是3个了

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