GWD 第一套 MTH 30 31 求解

luyi1988 · 发表于 2010-7-2 09:12:16

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.
这题答案是D，我觉得应该是A
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Q31:
A positive integer n is said to be “prime-saturated” if the product of all the different positive prime factors of n is less than the square root of n. What is the greatest two-digit prime-saturated integer?

99
98
97
96
95
这题就没有思路了

waigedet · 发表于 2010-7-2 09:19:08

Q30在OG12版有~答案是A没错
Q31你要把答案做因式分解~然后找出因数为质数~相乘小於答案开根号的

luyi1988 · 发表于 2010-7-2 09:24:18

了解了，3Q

yzha422 · 发表于 2010-7-2 09:38:22

31的答案是96吗

typhoidX · 发表于 2010-7-2 12:26:24

我见到过很多题，可以用一个公式解两个未知数，Q30这个邮票题看起来也是这样的。有了条件1，我们只有15X+29Y=440分钱。

想请教大家怎么能看出来在什么情况下可以只用一个公式？

lisa78 · 发表于 2010-7-2 12:59:05

弱弱的问一句，30题条件1的话，是15X+29Y=440，怎么求出答案的啊。。。。

lisa78 · 发表于 2010-7-2 16:11:23

把这道题顶上来，求解，是因为xy都是整数么，不是很好求解啊。。。

lisa78 · 发表于 2010-7-2 16:13:13

恩，是这样的，因为xy必须是整数，所以y只能是10，而x求出来也是10。因为x=490-29*y，所以490-29*y必须尾数至少是0,5，这样的话，y不是5，就是10，带进去，y只能是10~bingo~

GWD 第一套 MTH 30 31 求解

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