And now the slider numerical analysis Mathematica code.

Manipulate[Nvalue = RStar*fp*ne*fl*fi*fc*L;
 Grid[{{"R* (Rate of star formation)", 
    RStar}, {"fp (Fraction of stars with planets)", 
    fp}, {"ne (Avg number of planets that can support life)", 
    ne}, {"fl (Fraction of planets where life develops)", 
    fl}, {"fi (Fraction of planets with intelligent life)", 
    fi}, {"fc (Fraction that develop communication technology)", 
    fc}, {"L (Length of time civilizations can communicate)", 
    L}, {"N (Number of civilizations)", Dynamic[Nvalue]}}], {RStar, 0,
   50, 1}, {fp, 0, 1, 0.01}, {ne, 0, 5, 0.1}, {fl, 0, 1, 0.01}, {fi, 
  0, 1, 0.01}, {fc, 0, 1, 0.01}, {L, 0, 10000, 100}]

Your comments will be appreciated.