BIDMAS
BIDMAS is the rule used to decide the correct order of operations in a calculation. Following the correct order avoids mistakes and ensures everyone gets the same answer.
B = Brackets
I = Indices
D = Division
M = Multiplication
A = Addition
S = Subtraction
Why BIDMAS matters
Without BIDMAS, the same calculation could give different answers.
Example 1: Without BIDMAS
Calculate:
3 + 4 × 5
Multiply first:
4 × 5 = 20
Then add:
3 + 20 = 23
The answer is 23.
Brackets first
Anything inside brackets must be done before the rest of the calculation.
Example 2: Brackets
Calculate:
(8 + 2) × 3
Do the brackets first:
10 × 3 = 30
Indices
Indices, or powers, are calculated after brackets.
Example 3: Indices
Calculate:
2 + 3²
Calculate the power first:
3² = 9
Now add:
2 + 9 = 11
Multiplication and division
Multiplication and division happen before addition and subtraction.
Example 4: Multiplication before addition
Calculate:
6 + 12 ÷ 3
Divide first:
12 ÷ 3 = 4
Then add:
6 + 4 = 10
Working left to right
Division and multiplication have equal priority, so work from left to right. The same applies to addition and subtraction.
Example 5: Left to right
Calculate:
20 ÷ 5 × 2
Work left to right:
20 ÷ 5 = 4
4 × 2 = 8
Mixed calculations
Example 6: Full BIDMAS example
Calculate:
5 + (6 - 2)² × 3
Brackets first:
(6 - 2) = 4
Indices:
4² = 16
Multiplication:
16 × 3 = 48
Addition:
5 + 48 = 53
A common mistake is adding before multiplying. In BIDMAS, multiplication and division happen before addition and subtraction.
Write each step clearly on a new line in non-calculator questions. This reduces mistakes and can earn method marks.
Video explanation
A short Worthing Maths Tutor video explanation for BIDMAS can be embedded here later to improve student engagement and time on page.
Practice questions
- Calculate 7 + 3 × 4.
- Calculate (9 - 5) × 6.
- Calculate 2² + 5.
- Calculate 18 ÷ 3 + 7.
- Calculate 4 + (8 ÷ 2)².
Answers
- 19
- 24
- 9
- 13
- 20
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