GWD 5的一道余数题

cll0503

What is the remainder when the positive integer n is divided by 3?

(1)  The remainder when n is divided by 2 is 1.

(2)  The remainder when n + 1 is divided by 3 is 2.

                  

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

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

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

D. EACH statement ALONE is sufficient.

E. Statements (1) and (2) TOGETHER are NOT sufficient.

这类题一直不知道该怎么解，大虾帮忙！

正确答案是B，我选了C，因为根据推算，这个数除以3的余数是0.为啥是B呢？

徐涅涅

2）The remainder when n + 1 is divided by 3 is 2.

通过条件2可以得出n+1=3a+2(a是整数)

从而n=3a+1

所以n除以3的余数为1  选b

余数题通常都用n=ab+c这样的形式解

希望有帮助！

cll0503

谢谢！