I would like to learn how to get an average using a formula for for varying
groups of numbers.
for example:

Surgeon Operation Operation Time in Minutes

A Hernia 38 (1st Occurence)
31 (2nd)
59 (3rd...etc)
28
22
39

so the average TIME IN MINUTES for that Hernia operation is 36.16 minutes

my question is...how do I write a formula to find the averages for Multiple
physicians doing Multiple procedures???