GMAT考题：OG2017Q-DS-228

GMAT考题

If a, b, c, and d are numbers on the number line shown and if the tick marks are equally spaced, what is the value of a + c ?

(1) a + b = -8

(2) a + d = 0

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

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

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

EACH statement ALONE is sufficient.

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

毕出

题目分析：

（1）条件1只给出了a+b的值，无法得知c的值，只有条件1无法求得a+c

（2）条件2只给出了a+d的值，无法得知c的值，只有条件2无法求得a+c

结合条件1和条件2，因为题目中说明点之间的间隔是相等的，所以由条件2的式子减条件1的式子得到d-b=8，d和b之间有2个间隔，所以相邻的点之间的间隔为4。设a+c=x，该式子减条件2的式子得到c-d=x，所以x=-4。

因此，本题答案为（C），两个条件结合起来才能解题，任何单独一个均不行。

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