统计学——基于R（第3版）（基于R应用的统计学丛书）作者：贾俊平 习题答案 第四章

load("C:/exercise/ch4/exercise4_1.RData")
exercise4_1

#4.1
sum(0.209,0.223,0.178,0.114)

sum(0.041,0.130)

sum(0.061,0.028,0.011,0.004,0.001)

#4.2

#(1)
dbinom(2,4,0.1)

#(2)
pbinom(1,4,0.1)


#4.3
#(1)

1-pnorm(510,mean=500,sd=20)

pnorm(450,mean=500,sd=20)-pnorm(400,mean=500,sd=20)

#(2)

pnorm(1.2,mean=0,sd=1)-pnorm(0,mean=0,sd=1)

pnorm(0,mean=0,sd=1)-pnorm(-0.48,mean=0,sd=1)

1-pnorm(1.2,mean=0,sd=1)

#(3)
qnorm(0.95,mean=0,sd=1)



#4.4
#(1)

pt(-1.5,df=15)

1-pt(2,df=20)

qt(0.05,df=30)

#（2）

pchisq(12,df=8)

1-pchisq(18,df=20)

qchisq(0.975,df=15)

#(3)

pf(3.5,df1=15,df2=10)

1-pf(3,df1=12,df2=8)

qf(0.975,df1=20,df2=16)
``

```handlebars
#4-5
#（1）正态分布，来自正态总体的样本
xx<-rnorm(5000,100,10)
x<-sample(xx,100,replace=T)
xy<-round(x,0)
par()
hist(xy,ylab="频率",xlab="样本均值的分布",labels=T,col="red",main="正态分布样本")


#（2）样本均值的分布，来自正态总体的样本
xx<-vector()
for(i in 1:100){
xx<-append(xx,mean(rnorm(n,50,10)))
}
par(mai=c(0.8,0.8,0.1,0.1))
hist(xx,breaks=8,ylab="频率",xlab="样本均值的分布",freq =FALSE,col="green",main="样本均值的分布")

#（3）样本比例的分布，来自任意总体的样本（二项分布总体）
par()
x0<-vector()
n=2
for(i in 1:100){
x=rbinom(100,n,0.5)
x0<-append(x0,round(length(which(x==1))/100,2))
}
hist(x0,prob=T,col="lightblue",main=paste("样本比例的分布","n=",n))

#（4）样本方差的分布，来自正态总体的样本

yy<-vector()
n=2
for(i in 1:1000){
yy<-append(yy,var(rnorm(n,50,10)))
}
par(mai=c(0.8,0.8,0.1,0.1))
hist(yy,ylab="频率",xlab="样本均值的分布",freq =FALSE,col="pink",main="样本方差的分布")
#curve(dnorm(x,100,10),add=T,col="red",lwd=1)