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BIDMAS Practice Questions Where Left to Right Gives the Wrong Answer

Twelve expressions chosen so working left to right fails, each solved one operation per line, including division before multiplication and a nested bracket.

مختصر جواب

BIDMAS sets the order of a calculation: brackets, then indices, then division and multiplication together working left to right, then addition and subtraction together working left to right. So 4 + 3 × 5 = 19, not 35, and 48 ÷ 6 × 2 = 16, not 4.

سوالات

  1. سوال 1بنیادی1 نمبر

    Work out 4 + 3 × 5.

    حل دیکھیں

    19

    1. Multiplication ranks above addition.
    2. 3 × 5 = 15.
    3. 4 + 15 = 19.
    4. Left to right would give 7 × 5 = 35.
  2. سوال 2بنیادی1 نمبر

    Work out 20 − 12 ÷ 4.

    حل دیکھیں

    17

    1. Division ranks above subtraction.
    2. 12 ÷ 4 = 3.
    3. 20 − 3 = 17.
    4. Left to right would give 8 ÷ 4 = 2.
  3. سوال 3بنیادی2 نمبر

    Work out 8 + 2 × (5 − 1).

    حل دیکھیں

    16

    1. Brackets first: 5 − 1 = 4.
    2. 8 + 2 × 4.
    3. Multiplication next: 2 × 4 = 8.
    4. 8 + 8 = 16. Left to right would give 10 × 4 = 40.
  4. سوال 4بنیادی2 نمبر

    Work out 6 × 2 + 8 ÷ 4.

    حل دیکھیں

    14

    1. Both the multiplication and the division rank above the addition, so do them first.
    2. 6 × 2 = 12.
    3. 8 ÷ 4 = 2.
    4. 12 + 2 = 14. Left to right would give 12 + 8 = 20, then ÷ 4 = 5.
  5. سوال 5بنیادی معیار2 نمبر

    Work out 48 ÷ 6 × 2.

    حل دیکھیں

    16

    1. Division and multiplication share a rank, so work left to right.
    2. 48 ÷ 6 = 8.
    3. 8 × 2 = 16.
    4. Doing the multiplication first because M comes before D in BIDMAS gives 48 ÷ 12 = 4, which is wrong.
  6. سوال 6بنیادی معیار2 نمبر

    Work out 5 + 2² × 3.

    حل دیکھیں

    17

    1. Indices first: 2² = 4.
    2. 5 + 4 × 3.
    3. Multiplication next: 4 × 3 = 12.
    4. 5 + 12 = 17. Left to right would square 7 to get 49, then × 3 = 147.
  7. سوال 7بنیادی معیار2 نمبر

    Work out (9 − 5)² ÷ 2.

    حل دیکھیں

    8

    1. Brackets first: 9 − 5 = 4.
    2. 4² ÷ 2.
    3. Index next: 4² = 16.
    4. 16 ÷ 2 = 8. Squaring the 9 and the 5 separately would give 81 − 25 = 56, then ÷ 2 = 28.
  8. سوال 8بنیادی معیار3 نمبر

    Work out 24 ÷ (8 − 2 × 3).

    حل دیکھیں

    12

    1. Work inside the bracket first, and the ranks still apply inside it.
    2. 2 × 3 = 6, so the bracket is 8 − 6 = 2.
    3. 24 ÷ 2 = 12.
    4. Simplifying the bracket left to right gives 6 × 3 = 18, then 24 ÷ (−10), which is not the intended sum.
  9. سوال 9مشکل3 نمبر

    Work out 100 − 4 × (3 + 2)².

    حل دیکھیں

    0

    1. Bracket first: 3 + 2 = 5.
    2. 100 − 4 × 5².
    3. Index next: 5² = 25.
    4. Multiplication next: 4 × 25 = 100.
    5. 100 − 100 = 0.
  10. سوال 10مشکل4 نمبر

    Work out 2 × [30 − (4 + 5) × 2].

    حل دیکھیں

    24

    1. Innermost bracket first: 4 + 5 = 9.
    2. 2 × [30 − 9 × 2].
    3. Inside the outer bracket, multiplication ranks above subtraction: 9 × 2 = 18.
    4. 30 − 18 = 12.
    5. 2 × 12 = 24.
  11. سوال 11مشکل3 نمبر

    Work out the fraction with 12 + 8 on top and 5 − 1 underneath.

    حل دیکھیں

    5

    1. A fraction bar brackets the whole of the top and the whole of the bottom.
    2. Top: 12 + 8 = 20.
    3. Bottom: 5 − 1 = 4.
    4. 20 ÷ 4 = 5.
    5. Typed into a calculator as 12 + 8 ÷ 5 − 1 it gives 12.6, which is a different calculation.
  12. سوال 12مشکل2 نمبر

    Work out 20 − 5 + 3.

    حل دیکھیں

    18

    1. Addition and subtraction share a rank, so work left to right.
    2. 20 − 5 = 15.
    3. 15 + 3 = 18.
    4. Doing the addition first because A comes before S in BIDMAS gives 20 − 8 = 12, which is wrong.

غلطیاں کہاں ہوتی ہیں

  • Working straight through from left to right, so 4 + 3 × 5 comes out as 35.
  • Treating BIDMAS as six ranks rather than four, so 48 ÷ 6 × 2 is answered as 4 and 20 − 5 + 3 as 12.
  • Applying an index to the wrong quantity, squaring 5 + 2 in 5 + 2² × 3, or squaring 9 and 5 separately in (9 − 5)².
  • Simplifying the contents of a bracket left to right, so 8 − 2 × 3 becomes 18 instead of 2.
  • Ignoring the fraction bar as a grouping symbol when transferring an expression to a calculator.

What BIDMAS gets wrong about itself

Read as six ranked steps, BIDMAS produces wrong answers. Division and multiplication share one rank and are done left to right; addition and subtraction share the rank below and are also done left to right. The acronym has to name them in some order, and the order it picks is not a priority.

This is why 48 ÷ 6 × 2 is 16 and not 4. Division comes first here because it comes first on the page, not because division outranks multiplication. The same trap sits under 20 − 5 + 3, which is 18: doing the addition first because A comes before S in the acronym gives 12.

Eleven of the twelve questions below punish reading left to right and ignoring the ranks. The last one punishes the opposite — taking BIDMAS too literally as six steps.

One operation per line

Every answer below is written with one operation carried out per line and everything else copied down unchanged. It looks slow and it is the fastest way to stop losing marks, because it makes each step separately checkable and it removes the temptation to do two things at once in your head.

It also fixes the most common cause of a lost mark in these questions, which is not the order at all — it is copying a number wrongly while rushing to the answer. If 100 − 4 × (3 + 2)² is written out as 100 − 4 × 5², then 100 − 4 × 25, then 100 − 100, then 0, there is nowhere for a digit to go missing.

Brackets that are not written as brackets

A fraction bar groups everything above it and everything below it, as if each had brackets round it. Typing (12 + 8) ÷ (5 − 1) into a calculator as 12 + 8 ÷ 5 − 1 is a different sum entirely, and the calculator will answer the one you typed.

A square root sign does the same job, and so does the bracket inside a bracket: in 2 × [30 − (4 + 5) × 2] the inner bracket is resolved first, then the multiplication inside the outer one, then the subtraction, and only then the multiplication by 2.

In England, the order of operations is introduced in Year 6, where pupils are expected to use it in calculations involving all four operations.

عام سوالات

Is it BIDMAS, BODMAS or PEMDAS?

They are the same rule with different local wording. The B or P is brackets or parentheses; the I or O or E is indices, "of", or exponents. PEMDAS is the American version and appears in SAT material. Whichever spelling is used, DM is one rank read left to right and AS is the rank below, also read left to right.

Why is 48 ÷ 6 × 2 equal to 16 and not 4?

Because division and multiplication have equal priority and are carried out in the order they appear. 48 ÷ 6 = 8 comes first because it is written first, then 8 × 2 = 16. The M sitting before the D in the acronym is only spelling; it does not promote multiplication above division.

Do calculators follow BIDMAS?

Modern scientific calculators do, and simple four-function calculators often do not — they apply each operation as you press it. That difference is worth testing on your own machine with 4 + 3 × 5: an answer of 19 means it follows the ranks, and 35 means it does not and every calculation needs bracketing by hand.

When do pupils in England learn the order of operations?

It is introduced in Year 6, where pupils use their knowledge of the order of operations in calculations involving all four operations. It then reappears constantly through secondary school, since substituting into a formula, expanding brackets and evaluating an expression all depend on it being automatic.

حوالہ جات

  1. National curriculum in England: mathematics programmes of study — Department for Education

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