# my first script

input <- mtcars[,c('wt','mpg')]
plot(x=input$wt, y=input$mpg, 
     xlab="weight",
     ylab="mileage", 
     xlim=c(2,5),
     ylim=c(10,35), 
     main="Weight to Mileage",
     col="blue",cex=2, 
     pch=21, bg="magenta", lwd=4)

p1 <- c(1.5,33)
p2 <- c(4.5,11)
x1 = p1[1]; y1 = p1[2]
x2 = p2[1]; y2 = p2[2]
m = (y2-y1)/(x2-x1)
x <- c(2,3,4,5)
y = y1 + m*(x-x1)

lines(x,y,col="hot pink",lwd=5)

wt_old=3; wt_new=0.7*wt_old;
sprintf("wt old = %2.1f, wt new = %2.1f", 
        wt_old, wt_new)

mpg_old = y1 + m*(wt_old-x1)
mpg_new = y1 + m*(wt_new-x1)
sprintf("mpg old = %2.1f, mpg new = %2.1f", 
        mpg_old, mpg_new)
mpg_inc = mpg_new-mpg_old
sprintf("mpg increase = %2.2f mpg",mpg_inc)
perc_mpg_inc = 100*(mpg_inc/mpg_old)
sprintf("mpg increase in percentage = %2.2f ",perc_mpg_inc)