问题 解答题

有一本《数学的奥秘》科普书,每本定价15元,某校九年三班的同学准备组织去购买.经了解,甲、乙两书店各有不同的优惠方案:在甲书店购买5本以上,超出部分按九折优惠;在乙书店购买10本以上,超出部分每本让利2元.

(1)若需购买20本,应去哪家书店能获得更大优惠;

(2)购买多少本时,去乙书店比甲书店能获得更大优惠?

答案

(1)当购买20本时,

在甲书店购书需付:15×5+(20-5)×0.9×15=277.5(元),

在乙书店购书需付:15×10+(20-10)×(15-2)=280(元),

∵280>277.5,

∴应去甲书店购买;

(2)设需购书x本,依题意知x>10,

在甲书店购书需付:[15×5-(x-5)×0.9×15]元,

在乙书店购书需付:[15×10+(x-10)×(15-2)]元,

由15×5-(x-5)×0.9×15>15×10+(x-10)×(15-2),

解得:x>25,

答:购买25本以上,去乙店能获得更大的优惠.

阅读理解

阅读理解。

     What would you do if you were ill? Of course, we would eat some medicines. The most

common disease in the world is the cold. It often starts with a sore throat. If you catch a cold,

you sneeze and your nose runs. You usually have a headache, too. Often you have a cough.

It's not a serious disease, but you can feel quite ill.

     There isn't a cure (良方) for a cold, but you can take medicines to make you feel better.

For example, you can take aspirin to get rid of your headache. It is good to rest and to drink

a lot of water, too. A doctor once told me, "With the right medicine, a cold will last for seven

days. With no medicine, it will go on for a whole week!"

     Where does our medicine come from? A long time ago, people understood that some plants

made them feel better when they were ill. They ate leaves, the roots, the fruit, or the seeds of

plants. For example, the juice of lemons makes a sore throat feel better.

     In modern times, scientists have looked at these plants, and found out which chemicals

(化学物质) are in them. Many of our medicines today are made from those chemicals. There

are some diseases which we can't cure (治愈) yet. Such as, AIDS, cancers...

     And nobody has found a cure for old age. But because of modern medicines, the average

person now lives longer than their grandparents.

1. How does a cold often start?

    _________________________________________

2. What is aspirin used to do?

    _________________________________________

3. How long does a cold usually last?

    _________________________________________

4. What makes a sore throat feel better?

    _________________________________________

5. What are modern medicines usually made from?

    _________________________________________

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