继续发问

syf1985085

1

Is x² +
    y² > 6?

(1)     (x + y)² > 6

(2)     xy = 2

                  

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.

不明白的是,第一个为什么不成立?

2

At a garage sale, all of the prices of the items sold were different.  If the price of a radio sold at the garage sale was both the 15th highest price and the 20th lowest price among the prices of the items sold, how many items were sold at the garage sale?

 

 

A.     33

B.     34

C.     35

D.     36

E.      37

题目不是读很明白

3

A car traveling at a certain constant speed takes 2 seconds longer to travel 1 kilometer than it would take to travel 1 kilometer at 75 kilometers per hour.  At what speed, in kilometers per hour, is the car traveling?

 

 

A.     71.5

B.     72

C.     72.5

D.     73

E.      73.5

At a garage sale, all of the prices of the items sold were different.  If the price of a radio sold at the garage sale was both the 15th highest price and the 20th lowest price among the prices of the items sold, how many items were sold at the garage sale?

 

 

A.     33

B.     34

C.     35

D.     36

E.      37

题目不是读很明白

3

A car traveling at a certain constant speed takes 2 seconds longer to travel 1 kilometer than it would take to travel 1 kilometer at 75 kilometers per hour.  At what speed, in kilometers per hour, is the car traveling?

 

 

A.     71.5

B.     72

C.     72.5

D.     73

E.      73.5

[此贴子已经被作者于2008-3-21 17:30:15编辑过]

syf1985085

总共三题...不知道为啥发完会重复...不好意思....

zacharyzhang

第一题的第一个条件，将x=1.25, y=1.25代入，(x+y)^2=6.25>6,但x^2+y^2=3.125<6；另外你自己在找一对x^2+y^2>6的数很容易了。因此条件1不充分。第二个条件，分别将x=2,y=1代入以及x=0.5,y=4代入，是否大于6仍然无法确认。最后两个条件合在一起看，x^2+y^2=(x+y)^2-2xy，虽然xy=2，但(x+y)^2可以小于10也可以大于10，因此仍然无法判断x^2+y^2是否大于6