Properties of a p.d.f.
 
1)     f(x) ≥ 0        for all x
 
2)     ∫  f(x) = 1     ( So the total area under the p.d.f. curve = 1 )
          ^{all x}
 
EXAMPLE: X is 'a randomly picked value between 0 and 1'
 
1)    f(x) = 1,    for 0 < x < 1          f(x) = 0,   otherwise
 
2)  
   Note: For continuous variables P(X=a) =0 since