sample1<-"http://kanggc.iptime.org/book/data/sample1.txt" 
sample_dat<-read.delim(sample1,header=T)
sample_dat
year<-sample_dat$year
gdp<-sample_dat$GDP
consumption<-sample_dat$consumption
min(gdp)
max(consumption)
mean(gdp)
mean(consumption)
median(gdp)
median(consumption)
quantile(gdp)
quantile(consumption)
var(gdp)
var(consumption)
sd(gdp)
sd(consumption)
summary(sample_dat)