How to Use BIDMAS — Order of Operations | KS3 Maths

Reading left to right, you'd do $2 + 3 = 5$, then $5 \times 4 = 20$. But that's wrong — the rule is that multiplication comes before addition, so you do $3 \times 4$ first:

$2 + 3 \times 4 \;=\; 2 + \underbrace{3 \times 4}_{12} \;=\; 2 + 12 \;=\; 14$

Fourteen. And brackets show exactly what each order really means. Going left to right secretly adds first — that's $(2 + 3) \times 4 = 20$. But the times sign binds the 3 and the 4 into one quantity, so the real sum is $2 + (3 \times 4) = 14$. Same numbers, completely different answer — which is why the order isn't optional.

When brackets are written for you, they go first — that's the top of the ladder. Do the inside, then multiply:

$(4 + 2) \times 5 \;=\; 6 \times 5 \;=\; 30$

Brackets are just a way of saying "do this bit first," so there's never any doubt about what to work out before the $\times 5$.

Now every rung in one question. Work down the ladder:

• Indices: $3^2 = 9$, so it becomes $20 - 12 \div 4 + 9$.
• Division: $12 \div 4 = 3$, giving $20 - 3 + 9$.
• Addition and subtraction share the bottom rung, so work left to right: $20 - 3 = 17$, then $17 + 9 = 26$.

$20 - 12 \div 4 + 3^2 \;=\; 26$