【OG20-P289-413题】If x is a positive integer, then is x prime?⑴ 3x+ _OG17新题

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【OG20-P289-413题】

If x is a positive integer, then is x prime?

⑴ 3x+ 1 is prime.

(2) 5x + 1 is prime.

A

Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
分析A选项
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B

Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
分析B选项
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C

BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
分析C选项
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D

EACH statement ALONE is sufficient.
分析D选项
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E

Statements (1) and (2) TOGETHER are NOT sufficient.
分析E选项
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当前版本由 huan~ 更新于2018-09-25 17:34:31 感谢由 huan~ 对此题目的解答所做出的贡献。

条件1：可以确定x是偶数，但是取值不止一个，例如2,4都符合，不充分

条件2：同理，取值不止一个，例如2,6都符合，不充分

结合：x的取值仍然是不唯一的，例如2,6,等，不充分

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夏夏夏筱染

质数：1 2 3 5 7 11 13 17.。。。。条件1: 3x+1为质数， 3x为偶数，（除了3x=1）则需x为偶数，偶数又分为2和其他偶数。 2是质数，不充分条件2同理可分成2和其他

0 0 回复 2019-08-07 11:57:36
920

可是两个合起来除了2还有别的解吗？

0 0 回复 2018-09-07 22:54:51
Xxxffll回复920

6

0 0 回复 2018-09-21 10:02:10
11

x = +ve integer (1) 3x + 1 is prime if 3x+1 = 7 = prime => x= 2 , which is prime if 3x+1 = 19 = prime => x = 6 , which is not a prime Not sufficient (2) 5x + 1 is prime if 5x + 1 = 11 = prime => x = 2 , which is prime if 5x + 1 = 31 = prime => x = 6 , which is not a prime Not sufficient Combining 1 and 2 , we get Still Not sufficient Answer E

0 0 回复 2017-11-19 04:40:54