The Order of Operations are rules which one must obey to calculate any sum or expression correctly. They are known by many acronyms, such as BIDMAS, PEDMAS and BODMAS and apply to all areas of Mathematics. These state you must calculate different parts of of expressions first before other parts. Multiplication and Division share the same priority as each other, as do Addition and Subtraction. So other acronyms or mnemonic devices are used such as PEMDAS and "Please Excuse My Dear Aunt Sally".
Different countries substitute the first two letters of the acronyms for the Order of Operations with different synonyms.
Typically, Order of Operations are:
Brackets (also Parentheses)
Indices (also Exponents)
Division (or Multiplication)
Multiplication (or Division)
Addition (or Subtraction)
Subtraction (or Addition)
Actual Order of Operations are as follows:
Grouping Symbols (Parentheses, Brackets, etc.)
Division / Multiplication
Addition / Subtraction