Before you begin
What you need: The four basic arithmetic operations.
- Apply brackets and powers before other operations
- Handle multiplication/division and addition/subtraction correctly
- Use the distributive law to reduce arithmetic
Understand the idea
Order is part of the meaning
An expression is a set of instructions. Brackets group operations; powers come next; multiplication and division follow; addition and subtraction come last.
Equal priority means left to right
Multiplication does not always come before division. They share a level, so 24 ÷ 6 × 2 is 4 × 2 = 8. Addition and subtraction also share a level.
Rearrange only with valid rules
The distributive law a(b + c) = ab + ac can simplify mental calculation. For example, 19 × 7 = (20 − 1) × 7 = 140 − 7. Subtraction and division cannot be freely reordered.
Follow the operation ladder
- Brackets
- Powers
- × and ÷ →
- + and − →
A method you can reuse
a × (b + c) = a × b + a × c
Distribution also works with subtraction: a(b − c) = ab − ac.- Simplify the innermost brackets, then evaluate powers.
- Do multiplication and division from left to right.
- Do addition and subtraction from left to right, and estimate to check.
Multiplying by 25 is the same as multiplying by 100 and dividing by 4. For example, 48 × 25 = 4800 ÷ 4 = 1200.
Worked examples
Read the question first. Try a step yourself, then compare your reasoning.
Bracket first
Simplify 18 + 6 × (5 − 2).
- 5 − 2 = 3.
- 6 × 3 = 18.
- 18 + 18 = 36.
A left-to-right test
Simplify 48 ÷ 6 × 4 + 3.
- 48 ÷ 6 = 8.
- 8 × 4 = 32.
- 32 + 3 = 35.
Mental multiplication
Calculate 99 × 16.
- Write 99 as 100 − 1.
- Distribute: 100 × 16 − 1 × 16.
- 1600 − 16 = 1584.
Check your understanding
Quick questions, with explanations. These are for self-study and do not affect your account score.
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