Let's say you want to find out how many inventory items are not profitable (total inventory minus profitable items) or how many employees are approaching retirement age (total employees minus employees under 55). There are several ways to subtract numbers.
What do you want to do?
Subtract numbers in a cell
To do this task, use the  (minus sign) arithmetic operator.
For example, if you type the following formula in a cell:
=105
The cell displays the following result:
5
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Subtract numbers in a range
To do this task, use the SUM function. Adding a negative number is the same as subtracting.
Note There is no SUBTRACT function in Excel. Use the SUM function and convert any numbers that you want to subtract to their negative values. For example, SUM(100,32,15,6) returns 77.
Example
The example may be easier to understand if you copy it to a blank worksheet.
How to copy an example
 Create a blank workbook or worksheet.
 Select the example in the Help topic.
Note Do not select the row or column headers.
Selecting an example from Help
 Press CTRL+C.
 In the worksheet, select cell A1, and press CTRL+V.
 To switch between viewing the results and viewing the formulas that return the results, press CTRL+` (grave accent), or on the Formulas tab, in the Formula Auditing group, click the Show Formulas button.

A 
Data 
15000 
9000 
8000 
Formula 
Description (Result) 
=A2A3 
Subtracts 9000 from 15000 (6000) 
=SUM(A2:A4) 
Adds all numbers in the list, including negative numbers (16000) 

How you use the SUM function
The SUM function adds all the numbers that you specify as arguments (argument: A value that provides information to an action, an event, a method, a property, a function, or a procedure.). Each argument can be a range (range: Two or more cells on a sheet. The cells in a range can be adjacent or nonadjacent.), a cell reference (cell reference: The set of coordinates that a cell occupies on a worksheet. For example, the reference of the cell that appears at the intersection of column B and row 3 is B3.), an array (array: Used to build single formulas that produce multiple results or that operate on a group of arguments that are arranged in rows and columns. An array range shares a common formula; an array constant is a group of constants used as an argument.), a constant (constant: A value that is not calculated. For example, the number 210 and the text "Quarterly Earnings" are constants. An expression, or a value resulting from an expression, is not a constant.), a formula (formula: A sequence of values, cell references, names, functions, or operators in a cell that together produce a new value. A formula always begins with an equal sign (=).), or the result from another function. For example, SUM(A1:A5) adds all the numbers that are contained in cells A1 through A5 (a range). For another example, SUM(A1, A3, A5) adds the numbers that are contained in cells A1, A3, and A5 (A1, A3, and A5 are arguments).
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