求助 GWD31-7 数学 不解~~~~~~

dolorez

Q10:
Is x < y ?
(1)      The ratio of x to y is  .
(2)      xy > 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.
为什么选答案选E呢？？？？

Q30:
There are 8 books on a shelf, of which 2 are paperbacks and 6 are hardbacks.  How many possible selections of 4 books from this self include at least one paperback?

A.    40
B.    45
C.    50
D.    55
E.    60
怎么答案会是50？？？应该是55吧。。。。。

Q35:
What is the greatest common factor of the positive integers j and k?
(1)      k = j + 1
(2)      jk is divisible by 5.
    
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.

sayysong

Q10 E
1）考虑正负号两种情况
2）只能知道XY同号而已。

Q30 D
全组合减去全hardbacks的组合，C(8,4) - C(6,4) = 55

Q35 A
（1）因为K不能被J的任意一个除了1以外的因数整除，可得两数的最大公约数为1。
(2)单独的话有很多可能。20*40, 40*80, etc