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**.