\begin{Schunk}
\begin{Sinput}
 rate <- 2
 upper <- 10
 xvals <- seq(0,upper,by=0.02)
 yvals1 <- dexp(xvals, rate=rate)
 plot (xvals, yvals1, type="l", xlab="x",ylab="probability")
 rate <- 1
 upper <- 10
 xvals <- seq(0,upper,by=0.02)
 yvals1 <- dexp(xvals, rate=rate)
 lines(xvals, yvals1, lty=2)
 rate <- 0.2
 upper <- 10
 xvals <- seq(0,upper,by=0.02)
 yvals1 <- dexp(xvals, rate=rate)
 lines(xvals, yvals1, lty=3)
 legend("topright", legend=as.expression(c(bquote(lambda == 2.0), bquote(lambda == 1.0),  bquote(lambda == 0.2))), lty=c(1,2,3))
\end{Sinput}
\end{Schunk}
