#1
library(UsingR)
data(Cars93)
dataset = Cars93
attach(Cars93)
dataset
?Cars93
#a

model1 = lm(MPG.highway~Horsepower)
summary(model1)
plot( Horsepower, MPG.highway)
abline(model1)

newdata = data.frame(Horsepower = 225)
predict(model1,newdata,interval="predict",level=0.95)

#b
model1 = lm(MPG.highway~Weight)
summary(model1)
plot( Weight, MPG.highway)
abline(model1)

newdata = data.frame(Weight = c(6400, 2524))
predict(model1,newdata,interval="predict",level=0.95)

#2
install.packages("TH.data")
data("bodyfat", package="TH.data")
dataset = bodyfat
attach(bodyfat)
dataset

model1 = lm(DEXfat~age+waistcirc+hipcirc)
summary(model1)

newdata = data.frame(age = 47, waistcirc = 67,hipcirc = 135 )
predict(model1,newdata,interval="predict",level=0.95)

#3
library(UsingR)
data(stud.recs)
dataset = stud.recs
attach(stud.recs)
dataset

model1 = lm(num.grade~sat.m)
summary(model1)