The 15 careless mistakes that cost PSLE Maths marks
“Careless” mistakes are rarely careless. They are habits: the same wrong move, made the same way, every time a question sets the same trap. Here is each one, what it looks like on your child’s script, and how to fix it.
Factors and multiples (HCF, LCM)
Your child uses the HCF when the question needs the LCM, or the other way round. How to tell them apart in PSLE word problems and fix the habit.
See the fix →Whole numbersCalculation slip
Your child uses the right method but slips on the arithmetic, like a missing zero in long division. How to spot calculation slips and cut them down.
See the fix →FractionsFraction of a remainder
Your child takes "2/3 of the remainder" as 2/3 of the whole and loses the marks. See why it happens and how to fix it at home with one question.
See the fix →FractionsSimplest form in final fraction answers
Your child gets 3/6 when the answer is 1/2. When the PSLE asks for simplest form, unsimplified fractions can cost the mark. How to build the habit.
See the fix →PercentagePercentage of a new total
When the total changes, your child still divides by the old one. See the PSLE percentage mistake in a worked example and how to fix it at home.
See the fix →PercentageFound the increase, not the new price
Your child finds the 15% increase but stops before the new price. Why it happens in PSLE percentage increase questions and how to fix it.
See the fix →RatioStopped at one part in ratio
Your child finds 1 unit in a PSLE ratio question and writes it as the answer. Why children stop early and simple ways to fix it at home.
See the fix →RateMinutes and hours in rate
Your child writes 2 h 30 min as 2.3 h and the rate per hour comes out wrong. Why it happens in PSLE rate questions and how to stop it.
See the fix →AlgebraCollecting like terms in algebra
Your child simplifies 7y + 5 − 3y − 8 to 4y + 3 and the sign is lost. Why PSLE algebra slips happen and simple ways to fix them at home.
See the fix →MeasurementLeft out the units
Your child writes 81 instead of 81 cm². Where the answer line does not print the unit, leaving it out can cost marks. How to make units a habit.
See the fix →MeasurementConverting units (kg, ℓ, m, cm³)
Your child divides by 100 instead of 1000 when changing cm³ to litres, and the answer is ten times too big. Why it happens and how to fix it.
See the fix →Area & volumeArea and perimeter formulas
Your child forgets the ½ in the triangle area formula, or mixes up area and perimeter. How the PSLE mistake looks and how to fix it at home.
See the fix →Area & volumeRadius and diameter in circles
Your child uses the diameter in the circle area formula and the answer is four times too big. Why it happens in PSLE circles and how to fix it.
See the fix →Geometry & anglesAngle facts (straight line, triangle, quadrilateral)
Your child puts the outside angle into the triangle sum and gets the wrong angle. See the PSLE geometry mistake and how to fix it at home.
See the fix →Average & dataAverage and total
Your child subtracts two averages and gets 2 kg when the answer is 52 kg. Why PSLE average questions trip children up and how to fix it.
See the fix →Careless mistakes in PSLE Maths, answered.
How do I stop my child making careless mistakes in PSLE Maths?
Find out which mistakes they are. Most children repeat the same two or three habits, such as answering the part the question did not ask for. Name the habit, show the right working, then practise questions that set the same trap until your child gets them right several times in a row.
Is it a careless mistake or a concept gap?
If your child can explain the right method when you point at the mistake, it is usually a habit. If they cannot, it is a gap in understanding and needs teaching first.
Do careless mistakes really cost that much?
A slip in the first part of a structured question can carry through to the later parts. In a 5-mark question, one habit can cost most of the marks.
Find the habits, then fix them: 3 right in a row.
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