问题 解答题

2010年1月1日,全球第三大自贸区-中国-东盟自由贸易区正式成立,标志着该贸易区开始步入“零关税”时代,广西某民营边贸公司要把240顿白砂糖运往东盟某国的A,B两地,现用大,小两种货车共20辆,恰好能一次性装完这批白砂糖.已知这两种火车的载重量分别为15吨/辆和10吨/辆,运往A地的运费为:大车630元/辆,小车420元/辆;运往B地的运费为:大车750元/辆,小车550元/辆.

(1)求这两种货车各用多少辆;

(2)如果安排10辆货车前往A地,其余货车前往B地,且运往A地的白砂糖不少于115吨,请你设计出使用总运费最少的货车调配方案,并求出最少总运费?

答案

(1)解法一:设大车用x辆,小车用y辆,依据题意,得

x+y=20
15x+10y=240

解得

x=8
y=12

∴大车用8辆,小车用12辆.

解法二:设大车用x辆,小车用(20-x)辆,依据题意,得

15x+10(20-x)=240,

解得x=8.

∴20-x=20-8=12(辆).

∴大车用8辆,小车用12辆.

(2)设总运费为W元,调往A地的大车a辆,小车(10-a)辆;

调往B地的大车(8-a)辆,小车12-(10-a)=(a+2)辆,

则W=630a+420(10-a)+750(8-a)+550(a+2).

即:W=10a+11300(0≤a≤8,a为整数).

∵15a+10(10-a)≥115,

∴a≥3.

又∵W随a的增大而增大,

∴当a=3时,w最小.

当a=3时,W=10×3+11300=11330.

因此,应安排3辆大车和7辆小车前往A地,安排5辆大车和5辆小车前往B地,最少运费为11330元.

阅读理解

阅读理解。

                                                 Wetlands! Valuable Resources on the Earth

    There are many wetlands in China and some of them have become the world's important wetlands. The

Chinese Yellow Sea Wetlands are among them. They are in Yancheng, Jiangsu Province. They are home for

many different kinds of animals. The world's largest Milu Deer Nature Reserve is in them. More than 700

Milu deer live freely there. There are not many red-crowned cranes in the world, but every winter you can

see some in the Red-crowned Crane Nature Reserve in the Yellow Sea Wetlands.

    The temperature in the wetlands is usually neither too high nor too low. There us a lot of rain and sunshine,

too. They are really good places for wildlife. Offering (提供) food and home for some special kinds of animals

is not the only reason why we need to protect wetlands. Wetlands are important because they also prevent

flood. But some people want to change the wetlands to make more space for farms and less space for wildlife.

Luckily, more and more people are beginning to realize the importance of wetlands and wildlife. Every year, on

February 2nd, many activities are held to tell people more about wetlands.

1. The Chinese Yellow Sea Wetlands are in the ______ of China. [ ]

A. east

B. south

C. west

D. north

2. Usually the weather in the wetlands is ______. [ ]

A. hot

B. pleasant

C. cold

D. dry

3. The World Wetlands Day is on ______.[ ]

A. April 22

B. June 25

C. February 2

D. March 22

4. We must protect wetlands because ______.[ ]

A. they are home for wildlife

B. they can offer food to animals

C. they can prevent flood

D. all of the above

5. Some people want to change ______ to make more space for farms. [ ]

A. lands

B. world

C. wildlife

D. wetlands

单项选择题