问一道Prep数学，考过的同学说这很像真题，请NN解答！ 谢谢！！！

bisujiangkai

Q5:

If b, c, and d
are constants and x² + bx + c = (x + d)² for all values of x, what is the value of c?
(1)     d = 3

(2)     b = 6

                 

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.







Q9:

If the average (arithmetic mean) of four different numbers is 30, how many of the numbers are greater than 30?

(1)     None of the four numbers is greater than 60.

(2)     Two of the four numbers are 9 and 10, respectively.

                 

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.





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














Q9:

If the average (arithmetic mean) of four different numbers is 30, how many of the numbers are greater than 30?

(1)     None of the four numbers is greater than 60.

(2)     Two of the four numbers are 9 and 10, respectively.

                 

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.





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

bisujiangkai

谢谢！ 大家一起努力！

wanzhe1023

说说这3个题 你是怎么做的吧。。都做错了呢~

-- by 会员 bisujiangkai (2009/11/2 22:54:41)

第一题：  x²+bx+c=x²+2dx+d² ? c=d²   b=2d, 知道这三个数中间任何一个都能算出来


第二题： 知道9 和10了，又没有大于60的数。  平均数30。所以 剩下俩数之和= 30×4-19=101; 又都小于60，如果一个小于30，那剩下一个就是101-30=71了，于小于60矛盾，所以一定要大于30，都要大于30


第三题： 30%的公的学习，70%的母的学习；迁徙成功的20%公的，80%母的。假设先的总数a，后来成功的总数b。ratio=(20%b / 30% a)  /  (80%b / 70%b)=7/12


本人也是菜鸟，刚刚准备了几天，错了楼主误怪

heypony

恩，DCB

第一题
x^2+bx+c=x^2+2dx+d^2
所以b=2d, c=d^2
两个条件都能求出，选D

第二题
列举法
对于第一个条件，大于30的数有可能为1个，2个或3个
对于第二个条件，大于30的数有可能为1个或2个
结合二个条件一起考虑，大于30的数只能为2个，比如9，10，41，60
选C

I第三题
(20%/30%) / (80%/70%) = 7/12
选B

黄伟

DCB

bisujiangkai

说说这3个题 你是怎么做的吧。。都做错了呢~

esheen

D C B~

bisujiangkai

能讲讲你的做法吗？

xz328

第九题 明显C 啊

dylan_cd

对，第一个应该是D，都能求出