The SUM function is the single most important function to know in Excel. SUM adds all the numbers that you specify as arguments.
Each argument can be a range, a cell reference, an array, a constant, a formula, or the result from another function. For example, SUM(B3:B9) adds all the numbers that are contained in
cells B3 through B9.
The cells or ranges you are summing do not have to be adjacent to one another. For another example, SUM(B3, C7, H25) adds the numbers that are contained
in cells B3, C7, and H25.