The 2 Most Important

Excel Functions AND
Formulas

SUMPRODUCT

AND

INDEX/MATCH

Lesson 9: Excel Spreadsheets Statistical Functions (83)

In annex 9 you have found a description of all 83 Excel functions in the "Statistical" category. Below is the list of the 7 most useful ones.  See more on the obsolete function COUNTIF in lesson 14, more on the MIN, MAX, SMALL, LARGE functions

LARGE, SMALL

And what if you want the second or third largest value or the second smallest value. Use LARGE and SMALL like this:
=LARGE(A1:A5,2), =LARGE(A1:A5,3), =SMALL(A1:A5,2)
You can use these functions with dates.

As a matter of facts you can forget about MIN and MAX with:
=LARGE(A1:A5,1), =SMALL(A1:A5,1)

COUNT and  COUNTA

If you want to count the number of cells that are not blank COUNT and COUNTA will return a different result if in one of the cells there is a text. OR A SPACE
=COUNT(A1:A5) will return 5 is only numbers OR DATES are present in cells A1 to A5 and 4 if there is a letter, an empty cell OR A SPACE in one of the cells. The SPACE thing is important to remember when you are importing data from an external source.
=COUNTA(A1:A5) will return 5 unless one of the cells is empty. If all the cells contain numbers, letters OR SPACES the result will be 5.

AVERAGE and AVERAGEA

Watch for dates! If you want the average of a range and there is a date within there is a problem because dates are numbers. If all the cells are dates, indeed you can calculate the average date of.... The difference between AVERAGE and AVERAGEA becomes evident when one of the cells contains a text OR A SPACE and don't forget the SPACE. A cell containing a space is NOT empty.