title: Defining exponential distribution in R to estimate probabilities
body: <p>I have a bunch of random variables <code>(X1,....,Xn)</code> which are i.i.d. <code>Exp(1/2)</code> and represent the duration of time of a certain event. So this distribution has obviously an expected value of 2, but I am having problems defining it in R. I did some research and found something about a so-called Monte-Carlo Stimulation, but I don't seem to find what I am looking for in it.</p>
  
  <p>An example of what i want to estimate is: let's say we have 10 random variables <code>(X1,..,X10)</code> distributed as above, and we want to determine for example the probability <code>P([X1+...+X10&lt;=25])</code>.</p>
  
  <p>Thanks.</p>