title: How to add mean to scatter plot in R?
body: <p>I have data in the form:  </p>
  
  <pre><code>Num Percent  
  5   9.44  
  4   19.7  
  4   10.64  
  4   10.81  
  4   10.97  
  4   11.35  
  3   13.18  
  3   24.54  
  3   24.99  
  3   12.95  
  3   13.17  
  3   24.29  
  3   13.81  
  3   13.93  
  3   27.87  
  3   13.26  
  2   41.41  
  2   34.19  
  2   41.6  
  2   19.31  
  2   34.4  
  2   38.72  
  2   18.16  
  2   36.28  
  2   18.95  
  2   18.49
  </code></pre>
  
  <p>I would like to plot the data such that, along with the plot of 'num'(x) and 'percent'(y), the mean at every point of the x axis (2,3,4,5) is added to the plot and a regression line based on the mean series is plotted.  </p>