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标题: 请教一道GWD数学 [打印本页]

作者: dominique11 时间: 2008-8-20 19:28
标题: 请教一道GWD数学

If x + y is an integer, is y an integer?

(1) x – y is an integer.

(2) x + 2y is an integer.

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.

作者: zoe31123 时间: 2008-8-20 20:59
B.1不充分，只知道x+y的值不知道x的值；2充分，x+y是整数x+y+y是整数那么y一定是整数因为整数加整数才能等于整数。供参考

[此贴子已经被作者于2008-8-20 21:15:19编辑过]

作者: 雅奇 时间: 2008-8-21 03:18

我的想法是这样的：

x+y= 某一整数 A

x-y=某一整数 B

把上式相加，则2x=某两整数之和，则x一定为整数，同样可得 y也是整数

所以我选 D

请多指教啊，我也只是推理

作者: xxy870128 时间: 2008-8-21 08:38
i would agree to B
suppose x=n.5 y=m.5 so choice 1 works and satisfies the question but y is not an integer

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