求救两道数学题（GWD的）

eliasfan · 发表于 2011-1-27 21:15:40

Q16:

If n is a positive integer and r is the remainder when (n-1)(n+1) is divided by 24, what is the value of r?

(1)2 is not a factor of n.

(2)3 is not a factor of n.

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.

How many seconds will it take for a car that is traveling at a constant rate of 45 miles per hour to travel a distance of 22 yards? (1 mile = 1,160 yards)

A. 8
B. 9
C. 10
D. 11
E. 12

Q14:

A total of 30 percent of the geese included in a certain migration study were male.If some of the geese migrated during the study and 20 percent of the migrating geese were male, what was the ratio of the migration rate for the male geese to the migration rate for the female geese?
[Migration rate for geese of a certain sex = (number of geese of that sex migrating) / (total number of geese of that sex)]

A.1/4

B.7/12

C.2/3

D.7/8

E.8/7

Answer:
这题思路是怎么样的？
求救啊！！！！

eliasfan · 发表于 2011-1-27 21:17:18

答案为C，C
但不知是怎么来的？

xianyunfeng · 发表于 2011-1-27 21:32:29

第二题，题目后面提供的数字是错的。。1mile=1760yards

gavensc · 发表于 2011-1-27 21:32:48

我先看一下第一题啊：

1）2) 单独不行你自己实验两个数就可以了简单

1）和2）一起考虑，既然n不是2也不是3的倍数，所以，只有两种可能了： n=6k+1 or n=6k+5 (比如，你看啊n=6K+2就不行，因为这样就是2的倍数了）

所以当n=6k+1， (n-1)(n+1) =n^2-1 =36k^2 + 12k k>=1的，这样，36k^2 + 12k=12（3k^2+k) 永远都有24这个factor，所以r =0

同理可以证明当n=6k+5

所以 r=0

gavensc · 发表于 2011-1-27 21:38:09

你第二题数对么，看着挺简单啊，我怎么算的是 44/29 秒，我晕。

gavensc · 发表于 2011-1-27 21:40:26

我晕 1mile=1760yards

那么 45 miles per hour = 45×1760 / 3600 = 22 yard / second

然后 22/ 22 =1

我算的是1 啊怎么晕

eliasfan · 发表于 2011-1-27 21:42:02

谢谢gavensc

eliasfan · 发表于 2011-1-27 21:42:27

不过还有一道题麻烦帮忙看一下
Last Sunday a certain store sold copies of Newspaper A for $1.00 each and copies of Newspaper B for $1.25 each, and the store sold no other newspapers that day. If r percent of the store’s revenues from newspaper sales was from Newspaper A and if p percent of the newspapers that the store sold were copies of newspaper B, which of the following expresses r in terms of p?

A.   100p / (125 – p)
B.   150p / (250 – p)
C.   300p / (375 – p)
D.   400p / (500 – p)
E.   500p / (625 – p)

eliasfan · 发表于 2011-1-27 21:43:09

这题答案为D
也不知道是怎么来的

gavensc · 发表于 2011-1-27 21:55:21

你确定你没又抄错题吧？

假设卖出a=100份（即使无所谓a是多少，最后能约掉）那么有p/100 ×100=p份的报纸B卖掉，然后卖掉的A报纸是100-p

那么总的revenue就是 1.25p+1*(100-p)=0.25p+100

r/100 * 【0.25p+100】 =1*(100-p) 解出来r就行了但是貌似没有答案。

求救两道数学题（GWD的）

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