问题 填空题
假设关于某设备的使用年限x和所支出的维修费用 y(万元),有如下的统计资料:
x23456
y2.23.85.56.57.0
若由资料可知y对x呈线性相关关系,且线性回归方程为y=a+bx,其中已知b=1.23,请估计使用年限为20年时,维修费用约为______.
答案

∵由表格可知

.
x
=
2+3+4+5+6
5
=4,

.
y
=
2.2+3.8+5.5+6.5+7.0
5
=5,

∴这组数据的样本中心点是(4,5),

根据样本中心点在线性回归直线上,

∴5=a+1.23×4,

∴a=0.08,

∴这组数据对应的线性回归方程是y=1.23x+0.08,

∵x=20,

∴y=1.23×20+0.08=24.68

故答案为:24.68

选择题
阅读理解

Taking away a city's rubbish is a big job. Every day trucks come into a city to collect it. Most rubbish is made up of things we can't eat or use. If we kept these things we would soon have a mountain of rubbish.

In some cities the rubbish is collected and taken outside of city to a dump. Often the city dump is placed where the ground is low or there is a big hole. The kitchen rubbish is broken into small pieces and sent into the sewage system. The sewage system takes away the used water from toilets, bathtubs and other places.

To keep mice and flies away, some earth is used to cover the newly dumped rubbish. Later, grass may be planted on the rubbish-filled land. Finally, a house or a school may be built there, and then you'd never know that this had once been an old rubbish dump.

In other cities the rubbish is burnt in special places. The fire burns everything but the metal.

Sometimes the metal can be used again in factories where things are made of metal. The food parts of rubbish are put in special piles where they slowly change into something called humus, which looks like black earth. It is rich with the kinds of things that feed plants and help them grow.

小题1:You can most probably read the passage in_______.

A.a science book

B.a TV guide

C.a history book

D.a telephone book小题2: The main idea of the passage is_______.

A.to let us know taking away rubbish is a big job

B.to explain the need for rubbish collection

C.to introduce different ways to treat rubbish

D.to tell people to take useful things out of rubbish小题3:The underlined word "sewage" in the passage means_______.

A.污水

B.香肠

C.垃圾

D.粪便小题4: How should we take care of a used metal box according to the passage?

A.By burning it off.

B.By putting it in water.

C.By throwing it away.

D.By reusing and recycling it.