Algebra/Chapter 1/Order of Operations

Algebra

1.5: Order of Operations

---

The Order of Operations is used when doing expressions with more than one operation (e.g., ×, +, -). These are rules so you only get one answer all the time.

Example: When faced with $4+2\times 3$, how do you proceed?

There are two ways:

$4+2\times 3=(4+2)\times 3$

$4+2\times 3=6\times 3$

$4+2\times 3=18$

or

$4+2\times 3=4+(2\times 3)$

$4+2\times 3=4+6$

$4+2\times 3=10$

This is confusing, so which is correct? (Parentheses, "(" and ")" are used to show what to do first)

In order to communicate using mathematical expressions we must agree on an order of operations so that each expression has only one value.

For the above example all mathematicians agree the correct answer is 10.

You're probably wondering what this order is.

The Standard Order of Operations

Evaluate expressions in this order.

• Parentheses or Brackets (evaluate what's inside them)
• Exponents
• Multiplication and/or division from left to right
• Addition and/or subtraction from left to right

An Easy Way of Remembering

Use this memory tool to help remember the order! Please Excuse My Dear Annoying Sister It is also commonly called by its acronym, PEMDAS.

An alternative form of this is; Brackets Indices Division or Multiplication Addition or Subtraction (BIDMAS).

Yet another way of remembering this is Brackets Orders Division Multiplication Addition Subtraction (BODMAS)

or Bring Our Dear Mother Along Saturday

Examples

Order of Operations - Examples

Expression	Evaluation	Operation
4 × 2 + 1	= 4 × 2 + 1	Multiplication
	= 8 + 1	Addition
	= 9
12 - 9 ÷ 3	= 12 - 9 ÷ 3	Division
	= 12 - 3	Subtraction
	= 9
2 × 9 ÷ 3	= 2 × 9 ÷ 3	Left to Right
	= 18 ÷ 3	division
	= 6
9 ÷ 3 × 3	= 9 ÷ 3 × 3	Left to Right
	= 3 ×3	multiplication
	= 9
3 + 12 ÷ (5 - 2)	= 3 + 12 ÷ (5 - 2)	Parentheses
	= 3 + 12 ÷ 3	Division
	= 3 + 4	Addition
	= 7
7 × 10 - (2 × 4)2	= 7 × 10 - (2 × 4)2	Parentheses
	= 7 × 10 - 82	Exponents
	= 7 × 10 - 64	Multiplication
	= 70 - 64	Subtraction
	= 6

---

Practice Problems

Note: the expressions in the following quiz, use an asterisk (*) to indicate multiplication ($\times$) between adjacent factors. This use of the asterisk is nearly ubiquitous with the various computer languages, as the times symbol is not an historically available keyboard character. Hand written expressions commonly use a small vertically centered dot (·) to indicate multiplication. Where unambiguous, multiplication is implied between factors and a symbol is extraneous.

Quiz

Evaluate the following expressions

1 Evaluate the numerical expression

$2+4*3=$

2 Evaluate the numerical expression

$2*4+3=$

3 Evaluate the numerical expression

$(2+4)*3=$

4 Evaluate the numerical expression

$9^{2}+1-7*(8+4)/2=$