NormInv  - Script and chart function
                NormInv() returns the inverse of the normal cumulative distribution for the specified mean and standard deviation.
Syntax:
NORMINV(prob, mean, standard_dev)
Return data type: number
Arguments:
| Argument | Description | 
|---|---|
| prob | A probability associated with the normal distribution. It must be a number between 0 and 1. | 
| mean | A value stating the arithmetic mean for the distribution. | 
| standard_dev | A positive value stating the standard deviation of the distribution. | 
This function 
 is related to the NormDist function in 
 the following way: 
If prob = NORMDIST(value, m, 
 sd), then NORMINV(prob, m, sd) = value
Limitations:
All arguments must be numeric, else NULL will be returned.