OpenOffice Calc, the spreadsheet program offered free of charge by openoffice.org, allows you to perform calculations on data entered into the spreadsheet.
You can use OpenOffice Calc formulas for basic number crunching, such as addition or subtraction, as well as more complex calculations such as payroll deductions or averaging a student's test results.
In addition, if you change the data, Calc will automatically recalculate the answer without you having to reenter the formula.
The following step by step example covers how to create and use a basic formula in OpenOffice Calc.
Entering the Data
The following example creates a basic formula. The steps used to create this formula are the same ones to follow when writing more complex formulas. The formula will add the numbers 3 + 2. The final formula will look like this:
= C1 + C2

Select the cell C1 and enter 3, then press Enter.

Select the cell C2 and enter 2, then press Enter.

Now select cell C3. This is where we'll enter the basic addition formula.

When creating formulas in Open Office Calc, you always start by typing the equals sign. Type it in the cell where you want the answer to appear.

Following the equals sign, we add in the cell references of the cells containing our data.
By using the cell references of our data in the formula, the formula will automatically update the answer if the data in cells C1 and C2 changes.
The best way of adding cell references is by using the mouse to select the correct cell. This method allows you to select with your mouse the cell containing your data to add its cell reference to the formula.

For basic addition, enter the + after the C1.

Now add the second cell to the formula. Select the cell C2 to add the second number.

Press Enter to complete the formula. You should see in the Formula bar above the worksheet the newly created formula, but in cell C3 will be the result of this formula.
Mathematical Operators in OpenOffice Calc Formulas
Creating formulas in OpenOffice Calc is not difficult. Just combine the cell references of your data with the correct mathematical operator.
The mathematical operators used in Calc formulas are similar to the ones used in math class.
 Subtraction  minus sign (  )
 Addition  plus sign ( + )
 Division  forward slash ( / )
 Multiplication  asterisk (* )
 Exponentiation  caret (^ )
OpenOffice Calc Order of Operations
If more than one operator is used in a formula, there is a specific order that Calc will follow to perform these mathematical operations. This order of operations can be changed by adding brackets to the equation. An easy way to remember the order of operations is to use the acronym:
B.E.D.M.A.S.
The Order of Operations is:
 Brackets
 Exponents
 Division
 Multiplication
 Addition
 Subtraction
How the Order of Operations Works
Any operation(s) contained in brackets will be carried out first followed by any exponents.
After that, Calc considers division or multiplication operations to be of equal importance, and carries out these operations in the order they occur left to right in the equation.
The same goes for the next two operations — addition and subtraction. They are considered equal in the order of operations. Whichever one appears first in an equation, either addition or subtraction, is the operation carried out first.