# 1
mean(ii$lbdhdd,na.rm=TRUE)

# 2
quantile(ii$lbdhdd,probs=seq(0.2,0.8,0.2),na.rm=TRUE)

# 3
hist(ii$lbdhdd) 

# 5
ggplot(aes(x=lbdhdd),data=ii)+geom_histogram(binwidth=5)

# 7
ii$hdlcat<-factor(ii$hdlcat,c('Low','Medium','High'))

#8
table(ii$hdlcat)           
table(ii$hdlcat,useNA='always')           

# 9
prop.table(table(ii$hdlcat))*100
prop.table(table(ii$hdlcat,useNA='always'))*100

# 10
tt<-t.test(ii$lbdhdd,mu=60)
tt

# 11
tt$statistic

# 12
paste('t=',round(tt$statistic,1),', df=',tt$parameter,sep='')