pp-t1-DS93

[Huang Hsin-Yi]

93.
If the integer n is greater than 1, is n equal to 2 ?

(1) n has exactly two positive factors.

(2) The difference of any two distinct positive factors of n is odd.

Ans:B

（1) 兩個正因數-insufficient
(2)n的兩個不同的因數其中一個是奇數-insufficient
eg. (5,2) n=10
(7,4) n=28
所以我選 E

[amazingslim]

(2)應該是說任兩個因子的差是奇數
每個數一定有分子1，所以其他分子一定是偶數
如果n=2，2-1=1
n=4,分子有1,2,4，4-2=2,差是偶數
以此類推
所以偶數裡只有2符合

(2)sufficient

[Huang Hsin-Yi]

原來是我題意弄錯
感謝