問一題數學題

[mega]

A positive integer with exactly two different divisors greater than 1 must be
(A)a prime
(B)an even integer
(C)a multiple of 3
(D)the square of a prime
(E)the square of an odd integer
from:錢永強GRE難題, section3 第19題

[zeppelin]

題目翻譯完應該就沒問題了:

一個正整數正好有兩個"不同於1"且"比1大"的因數必是:

答案是 D

[mega]

= =經過你的翻譯,我一直想當初是怎麼看不懂得ㄏㄏ
我想再問一題
The "reflection" of a positive integer is obtained by reversing its digits. For example, 321 is the reflection of 123.
The difference between a five-digit integer and its reflection must be divisible by which of the following?
(A)2 (B)4 (C)5 (D)6 (E)9
Ans:E
from:PP2
感謝喔

[機車小邱]

The "reflection" of a positive integer is obtained by reversing its digits. For example, 321 is the reflection of 123.
The difference between a five-digit integer and its reflection must be divisible by which of the following?
(A)2 (B)4 (C)5 (D)6 (E)9
Ans:E
from:PP2
感謝喔

five-digit integer = a + 10b + 100c + 1000d + 10000e
its reflection = 10000a + 1000b + 100c + 10d + e
difference = - 9999a - 990b + 990d +9999e