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Formulas
As seen in the beginners guide you can enter in operators such as + - / and *. Formulas must start with a = and can use brackets.
The Use of Brackets
Brackets are used in excel to determine which operator to use first.
For example:
=(A1+A2)*10
In the above example the brackets sum A1 with A2 before multiplying by 10.
Note that a formula does not need to contain a cell reference. It could purely have a formula containing numbers.
For example:
=10*12-2