x <- 1:80
y <- seq(1, 300, 10) + rnorm(80) 

y[5] <- y[5] + 10
y[10] <- y[10] + 5
y[25] <- y[25] - 10

fit <- lm(y ~ x)
plot(fit)

x <- 1:50
y <- seq(1, 300, 10) + rnorm(50) 

y[2] <- y[2] + 10
y[10] <- y[10] + 5
y[25] <- y[25] - 10

fit <- lm(y ~ x)
plot(fit)