The distinguishing feature of a spreadsheet program such as Excel
is that it allows you to create mathematical formulas and execute
functions. Otherwise, it is not much more than a large table for
displaying text. This page will show you how to create these calculations.
Formulas
Formulas are entered in the worksheet cell and must begin with
an equal sign "=". The formula then includes the addresses
of the cells whose values will be manipulated with appropriate operands
placed in between. After the formula is typed into the cell, the
calculation executes immediately and the formula itself is visible
in the formula bar. See the example below to view the formula for
calculating the sub total for a number of textbooks. The formula
multiplies the quantity and price of each textbook and adds the
subtotal for each book.
Linking Worksheets
You may want to use the value from a cell in another worksheet
within the same workbook in a formula. For example, the value of
cell A1 in the current worksheet and cell A2 in the second worksheet
can be added using the format "sheetname!celladdress".
The formula for this example would be "=A1+Sheet2!A2"
where the value of cell A1 in the current worksheet is added to
the value of cell A2 in the worksheet named "Sheet2".
Relative, Absolute, and Mixed Referencing
Calling cells by just their column and row labels (such as "A1")
is called relative referencing. When a formula contains relative
referencing and it is copied from one cell to another, Excel does
not create an exact copy of the formula. It will change cell addresses
relative to the row and column they are moved to. For example, if
a simple addition formula in cell C1 "=(A1+B1)" is copied
to cell C2, the formula would change to "=(A2+B2)" to
reflect the new row. To prevent this change, cells must be called
by absolute referencing and this is accomplished by placing
dollar signs "$" within the cell addresses in the formula.
Continuing the previous example, the formula in cell C1 would read
"=($A$1+$B$1)" if the value of cell C2 should be the sum
of cells A1 and B1. Both the column and row of both cells are absolute
and will not change when copied. Mixed referencing can also
be used where only the row OR column fixed. For example, in the
formula "=(A$1+$B2)", the row of cell A1 is fixed and
the column of cell B2 is fixed.
Basic Functions
Functions can be a more efficient way of performing mathematical
operations than formulas. For example, if you wanted to add the
values of cells D1 through D10, you would type the formula "=D1+D2+D3+D4+D5+D6+D7+D8+D9+D10".
A shorter way would be to use the SUM function and simply type "=SUM(D1:D10)".
Several other functions and examples are given in the table below:
Function 
Example 
Description 
SUM 
=SUM(A1:100) 
finds the sum of cells A1 through A100 
AVERAGE 
=AVERAGE(B1:B10) 
finds the average of cells B1 through B10 
MAX 
=MAX(C1:C100) 
returns the highest number from cells C1 through C100 
MIN 
=MIN(D1:D100) 
returns the lowest number from cells D1 through D100 
SQRT 
=SQRT(D10) 
finds the square root of the value in cell D10 
TODAY 
=TODAY() 
returns the current date (leave the parentheses empty) 
Function Wizard
View all functions available in Excel by using the Function Wizard.
 Activate the cell where the function will be placed and click
the Function Wizard button on the standard toolbar.
 From the Paste Function dialog box, browse through the
functions by clicking in the Function category menu on
the left and select the function from the Function name
choices on the right. As each function name is highlighted a description
and example of use is provided below the two boxes.
 Click OK to select a function.
 The next window allows you to choose the cells that will be
included in the function. In the example below, cells B4 and C4
were automatically selected for the sum function by Excel. The
cell values {2, 3} are located to the right of the Number 1
field where the cell addresses are listed. If another set of cells,
such as B5 and C5, needed to be added to the function, those cells
would be added in the format "B5:C5" to the Number
2 field.
 Click OK when all the cells for the function have been
selected.
Autosum
Use the Autosum function to add the contents of a cluster of adjacent
cells.
 Select the cell that the sum will appear in that is outside
the cluster of cells whose values will be added. Cell C2 was used
in this example.
 Click the Autosum button (Greek letter sigma) on the
standard toolbar.
 Highlight the group of cells that will be summed (cells A2 through
B2 in this example).
 Press the ENTER key on the keyboard or click the green
check mark button on the formula bar .
