I'm trying to put the legend for my density plot with the theoretical plot in the histogram.

```
## lambda is 5
lambda <- 5
## the number of simulations is 20,000
nsim <- 20000
## the number of exponentials is 30
n_30 <- 30
## 20,000 simulations are run and a histogram of the results is generated
mns = NULL
for (i in 1 : nsim) {
mns <- c(mns, mean(rexp(n_30, lambda)))
}
hist(mns, col = "grey", main = "Frequency Distribution of Means of 30 Exponentials")
mean(mns)
## load the ggplot2 package
library(ggplot2)
data <- as.data.frame(mns)
## plot histogram with an overlay of the theoretical and sample distribution
plot <- ggplot(data, aes(x = mns))
plot <- plot + geom_histogram(aes(y=..density..), colour="black", fill="white")
plot <- plot + geom_density(aes(color = "Simulated"), size = 1.0, linetype="dashed")
plot <- plot + stat_function(aes(colour = "Normal"), fun = dnorm,
args = list(mean = mean(mns), sd = sd(mns)),
color = "blue",
size = 1.0, show.legend = TRUE)
plot <- plot + labs(title = "Sample vs. Theoretical Distributions of Means of 30 Exponentials",
x = "Means of exponential distributions",
y = "Density") + scale_colour_manual("Lgend title", values = c("red", "blue"))
print(plot)
```

However, when I run this code in my RMarkdown, the legend for stat_function (Normal) is not showing correctly. Can anybody help on this?

Thank you.