Topics › KS3 › Number

Order of operations

1. ooo-01 Present from here

   Work out $15 - 3 \times 4 + 1$

   A Option A: $4$

   B Option B: $49$

   C Option C: $2$

   D Option D: $60$
   Answer and misconceptions

   A Option A: $4$ ✓ Correct

   B Option B: $49$ ✗

   Works strictly left to rightDoes 15 - 3 = 12, then x 4 = 48, then + 1.

   C Option C: $2$ ✗

   Does addition before subtractionReads BIDMAS literally: 15 - (12 + 1) = 2.

   D Option D: $60$ ✗

   Does adding and subtracting before multiplyingWorks out 15 - 3 and 4 + 1 first, then multiplies: 12 x 5.
2. ooo-02 Present from here

   Work out $2 + 3(5 - 1)$

   A Option A: $20$

   B Option B: $14$

   C Option C: $9$

   D Option D: $16$
   Answer and misconceptions

   A Option A: $20$ ✗

   Adds before multiplyingWorks out 2 + 3 = 5 first, then multiplies by the bracket (4).

   B Option B: $14$ ✓ Correct

   C Option C: $9$ ✗

   Thinks a number next to a bracket is addedReads 3(4) as 3 + 4, giving 2 + 3 + 4.

   D Option D: $16$ ✗

   Ignores the bracketsWorks out 2 + 3 x 5 - 1 = 16.
3. ooo-03 Present from here

   Work out $4 + 2 \times 3^2$

   A Option A: $54$

   B Option B: $40$

   C Option C: $16$

   D Option D: $22$
   Answer and misconceptions

   A Option A: $54$ ✗

   Adds before multiplyingSquares correctly but then works out (4 + 2) x 9.

   B Option B: $40$ ✗

   Multiplies before applying the powerWorks out (2 x 3) squared = 36, then adds 4.

   C Option C: $16$ ✗

   Thinks squaring means multiplying by 2Treats 3 squared as 6, giving 4 + 2 x 6.

   D Option D: $22$ ✓ Correct
4. ooo-04 Present from here

   Work out $\dfrac{12 + 8}{4}$

   A Option A: $14$

   B Option B: $11$

   C Option C: $5$

   D Option D: $0.2$
   Answer and misconceptions

   A Option A: $14$ ✗

   Divides only the last number on topDoes not treat the fraction bar as a bracket: 12 + 8/4.

   B Option B: $11$ ✗

   Divides only the first number on topWorks out 12/4 + 8, forgetting the whole numerator is divided.

   C Option C: $5$ ✓ Correct

   D Option D: $0.2$ ✗

   Divides the bottom by the topWorks out 4 / 20, reading the fraction upside down.
5. ooo-05 Present from here

   Work out $36 \div 3 \times 2 + 2$

   A Option A: $26$

   B Option B: $8$

   C Option C: $48$

   D Option D: $3$
   Answer and misconceptions

   A Option A: $26$ ✓ Correct

   B Option B: $8$ ✗

   Does multiplication before divisionReads the M before the D in BIDMAS: 36 / (3 x 2) + 2.

   C Option C: $48$ ✗

   Does addition before multiplicationWorks out 2 + 2 first, then 12 x 4.

   D Option D: $3$ ✗

   Works from right to leftDoes 2 + 2 = 4, then 3 x 4 = 12, then 36 / 12.