BIDMAS - Order of Operations

BIDMAS stands for Brackets, Indices, Division, Multiplication, Addition, Subtraction. It is the order in which to work through a calculation: brackets first, then indices such as powers and roots, then division and multiplication, which share a level, then addition and subtraction, which share a level too. The letters are the easiest way to remember the order.

Yes. BODMAS and BIDMAS are the same rule with one letter changed: the O stands for Orders, another word for indices such as squares and square roots. So BODMAS is Brackets, Orders, Division, Multiplication, Addition, Subtraction. Whichever word your school uses, the order of the steps is identical.

Work through the letters in order. Buying a £300 phone and three £20 accessories, paid over 12 months, is (300 + 20 × 3) ÷ 12. Brackets first, and inside them multiplication before addition: 20 × 3 = 60, then 300 + 60 = 360. Then divide: 360 ÷ 12 = £30 a month. Skipping the order gives the wrong answer.

Neither. Division and multiplication share the same level in BIDMAS, so you work them from left to right in the order they appear: in 20 ÷ 5 × 2, divide first to get 4, then multiply to get 8. Addition and subtraction share a level in the same way: 10 − 6 + 3 is 4, then 7.

Start with the innermost brackets and work outwards. In 50 − 2 × (2 + 4 × 5) − 3, the innermost bracket gives 4 × 5 = 20 and then 2 + 20 = 22. Remove that bracket, multiply 2 × 22 = 44, subtract 3 to get 41, and finally 50 − 41 = 9. Only after the brackets are gone do the remaining BIDMAS steps apply.

UK schools use BIDMAS or BODMAS; PEMDAS is the American version of the same rule: Parentheses, Exponents, Multiplication, Division, Addition, Subtraction. Parentheses are brackets and exponents are indices, so the steps are identical. Multiplication and division still share a level, as do addition and subtraction, so the answers come out the same.