Mathematics

Decimals

The most common mistakes Singapore primary students make in Decimals, distilled from 149+ MOE-aligned questions across P4, P5. Free practice at every level.

From the question bank

Top 10 mistakes in Decimals

  1. #1Partial logic

    Not simplified.

    Seen in 4 questions

  2. #2Misconception

    Did not round.

    Seen in 2 questions

  3. #3Calc error

    This divides 75 by 25 correctly (75 ÷ 25 = 3) but divides 100 by 20 instead of 25 (100 ÷ 20 = 5). Both numerator and denominator must be divided by the same number.

    Seen in 1 question

  4. #4Misconception

    This writes the digits 7 and 5 as numerator and denominator without using place value. 0.75 has two decimal places so the denominator must be 100.

    Seen in 1 question

  5. #5Partial logic

    0.75 = 75/100 is correct as a fraction but not in simplest form. Divide both numerator and denominator by their HCF of 25: 75 ÷ 25 = 3 and 100 ÷ 25 = 4, giving 3/4.

    Seen in 1 question

  6. #6Calc error

    Divided by 100 instead of 1000.

    Seen in 1 question

  7. #7Calc error

    Divided by 10000 instead of 1000.

    Seen in 1 question

  8. #8Misconception

    Divided by 10 instead of 1000.

    Seen in 1 question

  9. #9Misconception

    Changed only the unit label without performing either conversion, leaving the number unchanged at 4.85.

    Seen in 1 question

  10. #10Calc error

    Correctly converted to mm (48.5 mm) but then divided by 100 instead of 1 000: 48.5 ÷ 100 = 0.485 m, confusing the mm-to-m factor with the cm-to-m factor.

    Seen in 1 question

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