问题 单项选择题

两家工厂A1和A2向三个零售店B1、B2和B3供应某种商品。A1和A2可供应的商品件数是200和300,而B1、B2和B3的需求量是100件、200件和50件。各工厂和零售店之间可以进行转运。如果运输的单位成本(以元件为单位)如下表所示(例如:表中第4列第3行的数字“5”表示将一件商品从A2运到B1的成本):

在最优的转运安排中,满足各零售店商品需求的运输总成本是()元。

A.1750

B.1550

C.1350

D.850

答案

参考答案:B

解析:

本题考查应用数学(运筹学—运输问题)基础知识。 暂时先不考虑可以转运的情况。 从A1和A2两厂发送到三个零售店B1、B2和B3的运输问题如下:

其中括号内的数字是运输的单位成本(单位:元/件)。 先建立初始方案如下:运费最便宜的是A2→B3,单位成本为每件3元。从B3的需求看,可以从A2供给B3所需的全部50件。从B2看,A2→B2的运费比A1→B2的运费便宜,所以A2→B2的运输应尽量多,根据合计的情况,不妨初步定为200件。这样,A2→B1就应是50件,A1→B1也应是50件,所建立的初始方案如下:

为了检查该方案能否改进,需要考虑如下两点: (1)如果A1→B2增加1件,则A2→B2就需要减少1件,A1→B1也需要减少1件,A2→B1就需要增加1件,总费用的增加量为+8-4-7+5=+2元。因此,A1→B2不能有运量。 (2)如果A1→B3增加1件,则A2→B3就需要减少1件,A1→B1也需要减少1件,A2→B1就需要增加1件,总费用的增加量为+9-3-7+5=+4元。因此,A1→B3不能有运量。 这样,在不考虑转运的情况下,该方案就是最优运输方案。运输的总成本为50×7+50×5+200×4+50×3=1550元。 为了考虑允许转运能否降低成本,需要将题中给出的表格图示如下:

从上图可以看出,A1→B1和A1→B2己不能通过转运降低成本,A1→B3则可以通过A1→B1→B3使每件运输降低1元成本。A2→B1、A2→B2和A2→B3都已不能通过转运降低成本。 由于在上面的方案中,A1→B3没有运量,因此没有必要通过转运来降低成本。所以本题的最优运输方案就是刚才做出的方案,不能改进了,最优的运输总成本为1550元。

完形填空
完形填空。
     Monty Robert's father was a horse trainer. As a child, Monty often went from one farm to another with 
 1  father. Sometimes they didn't have enough money to  2  for food, but Monty still kept hoping to own a
  3  farm.
     When he was in school, his teacher asked him to write a paper about what he wanted to be and do when
he grew up. He wrote a seven-page paper talking about his dream of having a horse farm one day. He  4  
drew a picture of a horse farm in the paper.
     The next day he handed it in to his teacher. Two days later, he  5  his paper back. On the front page was
a large red “F” with some words “See me after class.” So the boy  6  and asked his teacher, “Why did I get
an F?” The teacher said, “This dream will not come  7  for a young boy like you.  8  a horse farm needs a lot
of money. You have to buy the land. You have to pay for a lot of things. There is no way you could ever do
it.” Then the teacher added, “If you write this paper again with a  9  dream, I will give you a good grade.”
     After school he thought about it  10 . At last, he decided to hand in the same paper, making no changes
at all. He wrote, “You can keep the F and I'll keep my  11 .” Many years later, Monty had his own 200 acres
(英亩) horse farm. His dream came true. So don't let anyone take  12  your dreams. Follow your dreams, no
matter what they are.
( )1. A. his      
( )2. A. look     
( )3. A. horse    
( )4. A. ever   
( )5. A. came   
( )6. A. did      
( )7. A. out    
( )8. A. Owning   
( )9. A. difficult
( )10. A. easily   
( )11. A. horse   
( )12. A. back    
B. her    
B. pay   
B. chicken
B. even    
B. went  
B. knew   
B. from  
B. Drawing 
B. high
B. hard  
B. land   
B. off  
C. hers   
C. wait    
C. pig    
C. never    
C. got   
C. noticed
C. true   
C. Asking   
C. bad   
C. heavily  
C. dream    
C. care   
D. him   
D. ask    
D. flower 
D. over     
D. ran    
D. saw   
D. down   
D. Writing                     
D. simple
D. hardly 
D. paper    
D. away  
单项选择题