问题 解答题
质检部门对甲、乙两种日光灯的使用时间进行了破坏性试验,10次试验得到的两种日光灯的使用时间如下表所示,问:哪一种质量相对好一些?
使用时间(小时)频数
21001
21102
21203
21303
21401
甲                                  
使用时间(小时)频数
21001
21101
21205
21302
21401
乙.
答案

1甲的平均使用寿命为:

.
x
=
2100×1+2110×2+2120×3+2130×3+2140×1
10
=2121(h),

甲的平均使用寿命为:

.
x
=
2100×1+2110×1+2120×5+2130×2+2140×1
10
=2121(h),

甲的方差为:

S2=

212+4×112+9×12+9×92+192
10
=129(h2),

乙的方差为:

S2=

2100×1+2110×1+2120×5+2130×2+2140×1
10
=109(h2),

.
x
=
.
x
,且S2>S2

∴乙的质量好一些.

阅读理解

阅读理解。

     When we look to the east of Shanghai, we are sure to see a beautiful tower, especially in the evening

when the lights are on. That is the Oriental Pearl TV Tower.

     The Oriental Pearl TV Tower is 468 meters high, the tallest in Asia (亚洲) and the third in the world.

It weighs 125,000 tons. We know the weight of the Eiffel Tower in Paris is only 7,000 tons.

     The Oriental Pearl TV Tower can help broadcasting (广播) and TV transmission (转播). There are

six high-speed elevators (电梯) in the Tower. People can go up and have a beautiful view (视野) of

Shanghai.

     There are eleven steel (钢) balls in the Tower. They look like 11 beautiful "pearls" in the sky. The

lowest one is 68 meters high and the highest pearl is called the Space Cabin. It is 343 meters high. Going

up from the Space Cabin, we can reach the top of the tower. If you'd like to spend a night in the Tower,

there are eleven hotels, KTV rooms and a disco hall.

   Today the Oriental Pearl TV Tower becomes a new symbol of Shanghai.

1. The Oriental Pearl TV Tower is _____ according to the passage.

A. the tallest in the world

B. the tallest only in China

C. the tallest in Asia

D. the heaviest in the world

2. The tower is _____.

A. higher than the Eiffel Tower

B. almost 470 meters high

C. 68 meters high

D. 7,000 tons

3. People call the tower "The Oriental Pearl TV Tower" may be because _____.

A. it is made up of 11 steel balls

B. it has 11 steel balls inside

C. it looks like a pearl in the sky

D. people can see 11 shining steel balls from outside

4. People like going up the top of the Tower to _____.

A. enjoy the beautiful city

B. spend a night

C. have a rest

D. sing and play in KTV rooms

5. Which of the following is NOT mentioned about the Tower in the passage?

A. The weight of the Tower.

B. The height of the Tower.

C. The functions (功能) of the Tower.

D. How many people visit the Tower every year.

单项选择题