GWD 5 -26

oumengling

Q26:

If r, s, and t are positive integers, is r + s + t even?

(1)     r + s is even.

(2)     s + t is even.

                  

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.

答案是E

我选的是C, 因为只有EVEN + EVEN = EVEN, ODD + ODD = EVEN,所以知道R+S AND S+T是因为可以确定的呀....能不能帮忙解释一下...

littlestoner

当r、s、t全部是奇数的时候，则三数之和是奇数，当r、s、t三数全是偶数的时候，则三数之和是偶数，所以无法判断。不知道我的理解对不对

karen_gao

此题考的是答案的唯一性。

 

知道R+S AND S+T是可以确定r + s + t ，但是答案却不唯一，既可能为奇数也可能为偶数，所以答案选E。