搜题请搜索小程序“爱下问搜题”
问题 解答题
在一个不透明的口袋里装有仅颜色不同的黑、白两种颜色的球20只，某学习小组做摸球实验．将球搅匀后从中随机摸出一个球，记下颜色，再把它放回袋中，不断重复，下表是活动进行中记下的一组数据
摸球的次数n1001502005008001000
摸到白球的次数m5896116295484601
摸到白球的频率
m
n
0.580.640.580.590.6050.601
（1）请你估计，当n很大时，摸到白球的频率将会接近______．
（2）假如你去摸一次，你摸到白球的概率是______，摸到黑球的概率是______．
（3）试估算口袋中黑、白两种颜色的球有多少只．
答案

答：（1）根据题意可得当n很大时，摸到白球的频率将会接近0.6；

（2）因为当n很大时，摸到白球的频率将会接近0.6；

所以摸到白球的概率是

3
5
；

摸到黑球的概率是

2
5

（3）因为摸到白球的概率是

3
5
，摸到黑球的概率是
2
5

所以口袋中黑、白两种颜色的球有白球是20×

3
5
=12个，

黑球是20×

2
5
=8个

单项选择题

下列舞蹈中，属于土家族民族舞蹈的是()。

A．舂米舞

B．竹竿舞

C．摆手舞

D．踩堂舞
查看答案
单项选择题

Optimism is the art of always seeing the glass half full (1) half empty, finding something positive in even the most (2) of situations and last but not least the ability to expect the best even if the chances are (3) . It enables you to try new things, deal with failure as a learning experience (4) a stopping point. In general optimism gives you a reason to live. The world would be a better place if it was full of optimism, (5) unfortunately the trend in today’s youth is (6) the opposite way. Today it is (7) to be pessimistic. One could spend hours discussing how we arrived at this point, (8) our youth refuses to smell the roses and instead prefers to (9) themselves on their own pessimistic (10) .

Optimism is not an (11) gift but rather a learned behavior (12) . Like most behaviors optimism is best learned by watching examples, (13) you. The first step in creating a generation of people with a positive outlook on life, is to (14) life on the bright side yourself. (15) it would be wrong to (16) your child from all negativity, it is important that you are not the (17) of doubts and worries. Finding something positive in a negative situation needs to be (18) Show how to make the best of things by always (19) the positive, by encouraging your child after a(n) (20) and by explaining over and over that failure is just a part of progress.

14（）

A.drill

B.implement

C.exercise

D.apply
查看答案