求助a math question from GWD

A researcher plans to identify each participant in a certain
medical experiment with a code consisting of either a single letter or a pair
of distinct letters written in alphabetic order.  What is the least number of letters that can
be used if there are 12 participants, and each participant is to receive a
different code?

A.     
4

B.     
5

C.     
6

D.    
7

E.     
8

Answer: B

A certain right triangle has sides of length x, y,
and z, where x < y < z.  If the area of this triangular region is 1,
which of the following indicates all of the possible values of y ?

A.     
y > root2

B.     

        root 3)/2< y <
root2

C.     
(root 2)/3< y <
root 3)/2

D.    

        root3)/4< y <
root2)/3

E.     
y < root3/4

Answer: A

Was the average (arithmetic mean) weight of the package
mailed at a certain post office yesterday greater than 600 grams?

(1)   The total weight of the packages mailed at
the post office yesterday was greater than 14,500 grams.

(2)
          Fewer than 25 packages were
mailed at the post office yesterday.

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.

Answer:  answer is
C, but according to 1 and 2, we could only know the mimum weight is 580, so
greater than 580 could be more than 600 or less than 600, so, should be unknow.

If 1m+41
        = 2, what is the value
of m ?

(1)
          m < 0

(2)
          m² + 8m
+ 12 = 0

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.

Answer: Why not A since m=-2

第一个题目，首先可以是单个字母，其次是两个字母，一共12人

反正数字都很小，就一个一个试试，先说4个

C（4，1）＋C（4，2）＝4＋6＝10〈12，所以不行

看5，C（5，1）＋C（5，2）＝5＋10＝15〉12可以了，所以选B

第2个题目，首先是一个直角三角形，面积＝1，由于x〈y〈Z，有一个原则叫做大角对大边，所以说x和y必然为直角边，那么X＊Y/2=1可以推出X＊y=2，假设这个三角形是等腰直角三角形，那么x和y相等，就是说X平方＝2，那么x就是根号2，但是事实上x小于y，所以x必然小于根号2，所以y大于根号2

第3个题目，题目说是否邮局昨天package的平均重量大于600gram？

条件（1）总重量大于14500grams，但是不知道一共有多少个package，所以求不出来

条件（2）package的个数小于25件

结合条件（1）和（2），它说总重量大于14500，假设14501，它说fewerthan25件，假设24，那么算一下平均会发现可以达到6＊＊，所以说可以判断，充分，选C，大于，和小于，没有说大于等于或者小于等于，所以等号取不到

最后一个题目是不是选E？由条件1得出m＝－2或者m＝6，由条件（2）得出同样结果，结合两个，还是不能得到唯一解，所以选E？哈哈，不客气了。

1m+41 = 2 是什么意思？？

还有根据条件2，m=-2  和m=-6！  楼上是不是算错了？