GWD5-math-30

joyce8861 · 发表于 2010-1-27 18:04:35

Q30:

Joanna bought only $0.15 stamps and $0.29 stamps. How many $0.15 stamps did she buy?

(1) She bought $4.40 worth of stamps.

(2) She bought an equal number of $0.15 stamps and $0.29 stamps.

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a

怎么想都不对啊

ryanxie · 发表于 2010-1-27 18:13:20

我也按照一般思路认为是C，看到答案才明白，有且仅有一种方式可以买到价值4.40的邮票。可以列出方程，然后带数字进去。

不妨都扩大100倍。
关键在于有个尾数9，要凑总数440的尾数0，选择是不多的，必须是10的倍数才可以。

尘未 · 发表于 2010-1-27 18:30:55

这个题妙，顶下~
15X+29Y=440--------------------没有公因子

fengranxu · 发表于 2010-1-28 03:36:33

对啊，就是把楼上列的式子取xy都是整数的解就行了

joyce8861 · 发表于 2010-1-28 12:46:49

有道理啊。。谢谢指教

GWD5-math-30

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