As with all basic math operations in Excel, if you wish to add two or more numbers in you will need to create a formula; this can quickly assist you when you need to quickly find the sum of a few digits.

**Note: **To add several numbers that are located in a single column or row in a worksheet, use the SUM Function, which offers a shortcut to creating a long addition formula.

**Important points to remember about Excel formulas:**

- Formulas in Excel always begin with an equal sign (
**=**). - The equal sign is always typed into the cell where you want the answer to appear.
- The addition sign in Excel is the plus symbol (
**+**). - The formula is completed by pressing the
**Enter**key on the keyboard.

### Use Cell Reference in Addition Formulas

In the example data given above, the first set of rows, **1-3**, use a formula that is located in **column C** in order to add together the data in **columns A and B**. In this particular case, the numbers were entered directly into an addition formula:

= 5 + 5

However, in r**ow 2** of the image this example shows how it is much better to instead first enter the data into worksheet cells and then use the addresses, or references, of those cells in the formula:

= A3 + B3

One advantage of using cell references rather than the actual data in a formula is that if at a later date it becomes necessary to change the data, it is a simple matter of replacing the data in the cell rather than rewriting the entire formula. Normally, the results of the formula will update automatically once the data changes.

### Entering Cell References With Point and Click

Although it is possible to type the above formula into cell **C3** and have the correct answer appear, it can be handier to use point and click to add the cell references to formulas in order to minimize the possibility of errors created by typing in the wrong cell reference.

Point and click simply** **involves clicking on the cell containing the data with the mouse pointer to add the cell reference to the formula, instead of manually typing it into the cell.

### Using the Addition Formula in Excel

To create the example we see above in **cell** **C3** is quite simple; it allows us to add together the values of **A3** and **B3**. Here is how you get started:

- Type an equal sign (
**=**) in**cell****C3**to begin the formula. - Click on
**cell A3**with the mouse pointer to add that cell reference to the formula after the equal sign. - Type the
**+**) into the formula after**A3***.* - Click on
**cell B3**with the mouse pointer to add that cell reference to the formula after the addition sign. - Press the
**Enter**key on the keyboard to complete the formula. - The answer
**20**should be present in**cell****C3**.

**Note**: Even though you see the answer in cell C3, clicking on that cell will display the formula in the formula bar above the worksheet.

### Changing the Formula

Sometimes it becomes necessary to change or alter a formula; if you need to correct or change a formula, two of the best options are:

**Double clicking**on the formula in the worksheet to place Excel in Edit**Clicking**once on the cell containing the formula and re-entering the entire formula.

### Creating More Complex Formulas

To write more complex formulas that include other mathematical operators, use the steps listed above to get started and then continue to add the correct mathematical operators followed by the cell references containing the new data.

**Important**: Before mixing different mathematical operations together in a formula, however, you must understand the order of operations that Excel follows when evaluating a formula.

### Creating a Fibonacci Sequence

A Fibonacci sequence, created by the twelfth-century Italian mathematician, Leonardo Pisano, forms a continuous series of increasing numbers. These series are often used to explain, mathematically, among other things, different patterns found in nature such as:

- The spiral shape of different sea shells.
- The arrangement of leaves on a tree branch.
- The reproduction pattern of bees.

After two starting numbers, each additional number in the series is the sum of the two preceding numbers. The simplest Fibonacci sequence, shown in the image above, begins with the numbers zero and one:

0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, 1597, 2584 …

### Fibonacci and Excel

Since a Fibonacci series involves addition, it can be easily created with an addition formula in Excel as shown in the image above.

The steps below detail how to create the simplest Fibonacci sequence using a formula. The steps involve creating the first formula in **cell A3** and then copying that formula to the remaining cells using the fill handle. Each iteration, or copy, of the formula, adds together the previous two numbers in the sequence.

**To create the Fibonacci series shown in the example:**

- In
**cell A1**type a zero (**0**) and press the**Enter**key on the keyboard. - In
**cell A2**type a**1**and press the**Enter**key. - In
**cell A3**type the formula**=A1 + A2**and press the**Enter**key. - Click on
**cell A3**to make it the active cell. - Place the mouse pointer over the fill handle — the black dot in the bottom right corner of
**cell A3**— the pointer changes to a black plus sign (**+**) when it is over the fill handle. - Click and hold on the
**fill handle**and drag the mouse pointer down to**cell A19**. **A31**should contain the number**2584**.