《2025年快乐过暑假江苏凤凰科学技术出版社八年级提优版》

6. 一只不透明的袋中装有8个白球和若干个红球,这些球除颜色外都相同,搅匀后每次随机从袋中摸出一个球,记下颜色后放回袋中. 通过大量重复摸球试验后发现,摸到白球的频率是0.4,则袋中约有红球12个.

答案： 12

7. 某射击队的甲、乙两名运动员在相同条件下进行射击,结果如下表：
|射击总次数n|10|100|200|500|1000|
|击中靶心次数m|甲|9|94|168|424|851|
||乙|8|b|176|454|898|
|击中靶心频率$\frac {m}{n}$|甲|0.9|0.94|0.84|0.848|0.851|
||乙|a|0.91|0.88|0.908|0.898|
(1)表中$a=$0.8,$b=$91.
(2)在此条件下,可以估计甲运动员击中靶心的概率为0.85,乙运动员击中靶心的概率为0.90(精确到0.01).
(3)若从甲、乙两名运动员中选择一名成绩优秀的运动员参加射击比赛,你认为选哪一名运动员更合适？请说明理由.
乙运动员更合适. 理由如下:
∵ $ 0.85 ＜ 0.90 $,
∴ 乙运动员更合适.

答案：
(1) 0.8 91
(2) 0.85 0.90
(3) 乙运动员更合适. 理由如下:
∵ $ 0.85 ＜ 0.90 $,
∴ 乙运动员更合适.

1. The man B in 1988. He B for over 30 years.
A.died; was dead
B.died; has been dead
C.was dead; has died
D.was dead; has been dead

答案： B

2. Tea was born in China over 4,000 years ago. Now it B part of people's life around the world.
A.became
B.has become
C.was becoming
D.become

答案： B

3. I D China for three months and this is the first time I've tried on hanfu.
A.have gone to
B.have been to
C.have arrived in
D.have been in

答案： D

4. The shopping mall D for two years.
A.opened
B.has opened
C.is opening
D.has been open

答案： D

5. —Why don't you visit the Confucius Temple with us?
—Because I ____Cthere many times.
A.have been to
B.have gone to
C.have been
D.have been in

答案： C