The strength in spreadsheets is the ability to use vectors
to cause one cell to affect another cell or cells
Numeric values in a worksheet can be added, subtracted, multiplied or divided by creating formulas
Use this example for formula demonstrations. All formulas start with the = sign, and are followed by cell addresses and mathematical operators.
= begins a formula. If the = sign is not present, formula entries are treated as text
(parentheses) are to establish precedent. The result is held as a subtotal for further calculations. Where parentheses are enclosed within parentheses, they are calculated from the inside set to the outside set.
cell reference is a location on the sheet containing a value to work with. Unless fixed by user input, all locations are vectors, relative to the location of the cell that contains the formula.
if you need to lock a formula reference to a specific location (or, said another way, to an absolute  not relative  cell reference), use the f4 key to append the $ sign to a cell reference to lock in a specific location
example:

$A1 refers ab$olutely to row A but only relatively to column 1
[column will vary] 
$A$1 refers ab$olutely to row A and ab$olutely to column 1
[there is nothing relative about this reference]
arithmetic operators
 + addition
  subtraction
 * multiplication
 / division
 ^ exponentiation
a numeric constant is a number that will remain the same until the value is changed in the future
functions
are terms that describe built in formulas that perform specialized arithmetic
range reference is the starting and ending cells of a group of cells and enclosed in parentheses. they are separated by colons if the cells are contiguous, or with a comma if they are noncontiguous
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Entering a Formula
To enter a formula in a cell, click on the cell, then transfer your attention to the formula bar
Click or type the = character, and then enter the formula. Remember to start all formulas and functions with the = sign.
Normally, formulas use cell references rather than numbers
 place the cell address of the cell that contains the number you want into the formula. That way, if the number changes, the formula remains correct.
 for example, =A1+B1 would add the numbers in cells A1 and B1 and put the answer wherever you entered this formula
 if you use cell addresses, you can change data later (e.g., data in B4), and then the number calculated by a formula will change automatically
However, you can use numbers in formulas
= D8*1.06
means
this formula equals
the contents of D8 multiplied by 1.06
When using the formula bar
 you can point to the cell you want
 type an operator
 point to the next cell
 OR enter the formula using the cell reference addresses
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Order of Precedence & Operations
(parentheses)
the result is held as a subtotal for further calculations.
Where parentheses are enclosed within parentheses,
they are calculated from the inside set to the outside set.
^ exponentiation,
/ division or
* multiplication
are calculated in the sequence entered from left to right
formulas are calculated left to right and parentheses are used to distinguish order
using 15/3+2 for example:
 15/3+2 = 7
 15 divided by three = five, and five plus two = seven
 or (15/3) + 2 = (5)+2 = 7
but
 fifteen divided by the result of three plus two = fifteen divided by five = three
 or 15/ (3+2) = 15/ 5 = 3
+ addition or
 subtraction
are calculated in the sequence entered from left to right
functions are calculated separately and included in the result depending on the adjacent arithmetic operators
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Edit Formulas
click in cell with formula or in the formula box
The same is true in Excel for Mac
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Techniques to Help Correct Errors in Data
Error Codes
 #### data is too wide for cell
 #N/A omitted a required argument in a function
 #REF the formula cannot find the cell included in the argument
 #VALUE the formula calls for a number or a value and the cell contains text
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Let the program work for you
to check for source of errors, use the Auditing Toolbar
The same is true in Excel for Mac
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