每次遇到都是很清楚如何解.
When positive integer x is divided by 5, the remainder is 3; and when x is divided by 7, the remainder is 4. When positive integer y is divided by 5, the remainder is 3; and when y is divided by 7, the remainder is 4. If x > y, which of the following must be a factor of x - y?
A. 12
B. 15
C. 20
D. 28
E. 35
答案: E
这种题有没有什么固定的思路呀...还是就是乱试...
两个数被5除，余数相同，那么这两个数相减，结果肯定是5的倍数；
同理，也是7的倍数
结合起来就可以确定答案e
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