In Excel, syntax for this function is NORMINV(probability,mean,standard deviation). Using the sales example, with a weekly sales average of $2,000 that fluctuates about $500 up or down, you know ...

Probability distribution functions (PDFs) describe the expected values of random variables drawn from a sample. The shape of the PDF explains how likely it is that an observed value might occur.

Probability distributions can also be used to create cumulative distribution functions (CDFs) that add up the probability of occurrences cumulatively. They always start at zero and end at 100%.