请教几道prep的数学题~

wwwjendy

是在模考时做错的，事后对这几道题还是没有头绪

题目是我从破解版里找出来的，不知道为什么没有答案。。。。

126.
                12631-!-item-!-187;#058&009380

9.4  9.9  9.9  9.9  10.0  10.2  10.2  10.5

The mean and the standard deviation of the 8 numbers shown are 10.0 and 0.3, respectively.  What percent of the 8 numbers are within 1 standard deviation of the mean?

 

(A) 90%

(B) 85%

(C) 80%

(D) 75%

(E) 70%

这道是什么意思一直没有看懂

155.
                    15795-!-item-!-187;#058&010817

If 500 is the multiple of 100 that is closest to x and 400 is the multiple of 100 that is closest to y, which multiple of 100 is closest to x + y ?

(1) x < 500

 

(2) y < 400

这道也是看不懂

215.
                        20830-!-item-!-187;#058&013425

On the number line, the distance between point A and point C is 5 and the distance between point B and point C is 20.  Does point C lie between point A and point B ?

(1)  The distance between point A and point B is 25.

(2)  Point A lies to the left of point B.

这道我用的是很复杂的一个一个分类讨论的方法，而且做出来prep还是判定我错

谢谢牛牛们~~~~~~

wwwjendy

还有一道

199.
                19170-!-item-!-187;#058&012498

Warehouse W's revenue from the sale of sofas was what percent greater this year than it was last year?

(1)  Warehouse W sold 10 percent more sofas this year than it did last year.

(2)  Warehouse W's selling price per sofa was $30 greater this year than it was last year.

这道是A么？好像当时也判我错的。。

owenwei

126.
                12631-!-item-!-187;#058&009380

9.4  9.9  9.9  9.9  10.0  10.2  10.2  10.5

The mean and the standard deviation of the 8 numbers shown are 10.0 and 0.3, respectively.  What percent of the 8 numbers are within 1 standard deviation of the mean?

 within 1 standard deviation of the mean ---- 10+/-0.3 , so the range is [9.7,10.3]

 within 1 standard deviation of the mean ---- 10+/-0.3 , so the range is [9.7,10.3]

8个数里有6个在这个范围里，所以是75%

(D) 75%

 

155.
                                15795-!-item-!-187;#058&010817

If 500 is the multiple of 100 that is closest to x and 400 is the multiple of 100 that is closest to y, which multiple of 100 is closest to x + y ?

 根据已知，x 属于(450,550) , y属于(350,450)，那么 x + y四舍五入至100的倍数 可能是800，900或者1000

(1) x < 500 ，可能是800或900，不确定

(2) y < 400，可能是800或900，不确定

两个条件加起来，800或者900页都有可能，还是不确定

比如x=451,y=351,x+y 取800，又比如x=499,y=399,x+y 取900

215.
                                20830-!-item-!-187;#058&013425

On the number line, the distance between point A and point C is 5 and the distance between point B and point C is 20.  Does point C lie between point A and point B ?
                                

(1)  The distance between point A and point B is 25.
                                

(2)  Point A lies to the left of point B.

 3个点有3种关系，a在中间,b在中间,c在中间，已知ac=5,bc=20,排除b在中间的可能性，所以只可能是a在中间或者c在中间

条件1说明一定是c在中间

条件2不充分，a在中间或者c在中间都有可能

199.
                                        19170-!-item-!-187;#058&012498

Warehouse W's revenue from the sale of sofas was what percent greater this year than it was last year?
                                        

(1)  Warehouse W sold 10 percent more sofas this year than it did last year.
                                        

(2)  Warehouse W's selling price per sofa was $30 greater this year than it was last year.

要知道数量的百分比变化，还要知道价格的百分比变化

条件1不够

条件2不够（知道单价贵了30元没有用处，要知道百分之多少变化才可以）

加起来还是不够

155.
            15795-!-item-!-187;#058&010817

If 500 is the multiple of 100 that is closest to x and 400 is the multiple of 100 that is closest to y, which multiple of 100 is closest to x + y ?

 根据已知，x 属于(450,550) , y属于(350,450)，那么 x + y四舍五入至100的倍数 可能是800，900或者1000

(1) x < 500 ，可能是800或900，不确定

(2) y < 400，可能是800或900，不确定

两个条件加起来，800或者900页都有可能，还是不确定

比如x=451,y=351,x+y 取800，又比如x=499,y=399,x+y 取900

215.
            20830-!-item-!-187;#058&013425

On the number line, the distance between point A and point C is 5 and the distance between point B and point C is 20.  Does point C lie between point A and point B ?
            

(1)  The distance between point A and point B is 25.
            

(2)  Point A lies to the left of point B.

 3个点有3种关系，a在中间,b在中间,c在中间，已知ac=5,bc=20,排除b在中间的可能性，所以只可能是a在中间或者c在中间

条件1说明一定是c在中间

条件2不充分，a在中间或者c在中间都有可能

199.
                    19170-!-item-!-187;#058&012498

Warehouse W's revenue from the sale of sofas was what percent greater this year than it was last year?
                    

(1)  Warehouse W sold 10 percent more sofas this year than it did last year.
                    

(2)  Warehouse W's selling price per sofa was $30 greater this year than it was last year.

要知道数量的百分比变化，还要知道价格的百分比变化

条件1不够

条件2不够（知道单价贵了30元没有用处，要知道百分之多少变化才可以）

加起来还是不够

payo

以下是引用owenwei在2009/9/20 14:53:00的发言：  

(2)  Warehouse W's selling price per sofa was $30 greater this year than it was last year.

(2)  Warehouse W's selling price per sofa was $30 greater this year than it was last year.

条件2不够（知道单价贵了30元没有用处，要知道百分之多少变化才可以）

加起来还是不够

原来是$30啊...这题错了两遍...review时看了几遍都看成30%...怎么都想不通...