curve(dt(x, 30), from = -5, to = 5, col = "orange", 
      xlab = "quantile", ylab = "density", lwd = 2)
curve(dt(x, 10), from = -5, to = 5, col = "red", add = TRUE, lwd = 2)
curve(dt(x, 5), from = -5, to = 5, col = "green", add = TRUE, lwd = 2)
curve(dt(x, 2), from = -5, to = 5, col = "black", add = TRUE, lwd = 2)
legend("topleft", legend = paste0("DF = ", c(2, 5, 10, 30)),
       col = c("black", "green", "red", "orange"),
       lty = 1, lwd = 2)