Excel functions for density and cumulative density normal distributions 
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  =norm.dist(x,mean,standard_dev,cumulative)

    x                is the input value
    mean:            is the mean of the normal distribution
   standard_dev      is the standard deviation 
   cumulative =TRUE  is for cumulative distribution 
              =FALSE is for probability mass function 
                     (density distribution funtion)

  Examples for standard normal density funtion
                      1                                     
           f(x) = --------- * exp(-0.5 *x^2)               
                   sqrt(2*pi)                                
  Example 1: x=0   
           -> f(x) = 1/sqrt(2*3.1415925) ->  0.3989423
           -> =NORM.DIST(0,0,1,FALSE)    ->  0.39894228

  Example 2: xx=1
           -> f(1) = 1/sqrt(2*3.1415926)*exp(-0.5) ->   0.2419707  
           -> ==NORM.DIST(1,0,1,FALSE)             -> 0.241970725

          Examples for cumulative normal distribution. 
          we know that a normal distribution is symmetric. 
          Thus, cumulative with x=0 should be 0.5

  Example 3: = NORM.DIST(0,0,1,TRUE)  -> 0.5           
  Example 4: = NORM.DIST(3,0,1,TRUE)  -> 0.998650102
  Example 5: = NORM.DIST(-3,0,1,TRUE) -> 0.001349898

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Excel functions related to normal distributions  
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 1)  =norm.dist(x,mean,standard_dev,cumulative)

     1A)  =norm.dist(x,mean,standard_dev,cumulative)

     1B)   =norm.dist(x,mean,standard_dev,TRUE)

 2)  =norm.inv(probability, mean,standard_dev)
     This formula and 1B) is a pair. 
      
       =norm.dist(x,mean,standard_dev,TRUE) -> p
       =norm.inv(p, mean,standard_dev)      -> x

       = NORM.DIST(0,0,1,TRUE)  -> 0.5  
       = norminv(0.5,0,1)       -> 0

       = NORM.DIST(0.23,0,1,TRUE)  -> 0.590954115
       = norminv(0.590954115,0,1)  -> 0.23

       =NORM.DIST(0.3,0.5,2.5,TRUE)  -> 0.468118628
       =NORMINV(0.468118628,0.5,2.5) -> 0.3

  3) =norm.s.dist()   for standard normal distribution 
  4) =norm.sinv() inverse of the standard normal distribution
  5) =normdist()   the same as norm.dist()
  6) =normssdist()  <=> norm.s.dist()
  7) =normSINV()    <=> norm.s.inv()   
     
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