What you need to know
When a calculation has more than one operation, everyone needs to do it in the same order or we would get different answers. That order is called BODMAS: Brackets, Orders, Division and Multiplication, Addition and Subtraction. Some schools say BIDMAS or BEDMAS (the I or E stands for indices or exponents). It is the same rule.
| Letter | Meaning | Example |
|---|
| B | Brackets first | (2 + 3) × 4 = 5 × 4 = 20 |
| O | Orders: powers and square roots | 32 = 9, so 32 + 1 = 10 |
| D and M | Division and multiplication, left to right | 12 ÷ 3 × 2 = 4 × 2 = 8 |
| A and S | Addition and subtraction, left to right | 10 − 4 + 3 = 6 + 3 = 9 |
The most important detail: D and M are a tie, and A and S are a tie. Division does not beat multiplication and addition does not beat subtraction. When you reach that level, simply work from left to right.
7 + 3 × 4
- No brackets, no powers. Multiplication comes before addition.
- 3 × 4 = 12.
- 7 + 12 = 19. (Not 40: you do not add first just because the + comes first.)
(7 + 3) × 4
- Brackets first: 7 + 3 = 10.
- 10 × 4 = 40.
- Same numbers as the last example, but the brackets change the answer.
20 − 8 ÷ 2 + 32
- Orders first: 32 = 9. The expression becomes 20 − 8 ÷ 2 + 9.
- Division next: 8 ÷ 2 = 4. Now it is 20 − 4 + 9.
- Addition and subtraction, left to right: 20 − 4 = 16, then 16 + 9 = 25.
36 ÷ (4 + 2) × 3
- Brackets first: 4 + 2 = 6. Now it is 36 ÷ 6 × 3.
- Division and multiplication are a tie, so go left to right: 36 ÷ 6 = 6.
- Then 6 × 3 = 18. (Not 36 ÷ 18 = 2, which is what you get if you multiply first.)
Common mistake: doing all the multiplication before any division, or all the addition before any subtraction. 36 ÷ 6 × 3 = 18, not 2, and 10 − 4 + 3 = 9, not 3. Ties are worked left to right.
Common mistake: adding brackets that are not there. 7 + 3 × 4 = 19. If the question wanted 40, it would have been written (7 + 3) × 4.
Check yourself
- 5 + 6 × 2 = ?
- (5 + 6) × 2 = ?
- 24 ÷ 6 × 2 = ?
- 18 − 2 × 3 + 4 = ?
- 42 − (9 − 5) × 2 = ?
- 50 − (3 + 2)2 ÷ 5 = ?
Answers: 1. 17 2. 22 3. 8 (24 ÷ 6 = 4, then 4 × 2) 4. 16 (18 − 6 + 4) 5. 8 (16 − 4 × 2 = 16 − 8) 6. 45 (50 − 25 ÷ 5 = 50 − 5)