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PSLE Maths careless mistake

Answered the part not asked for

This is the mistake that hurts most, because the working is perfect. The bar model is right, every unit is right, and the number written on the answer line is the wrong one: a part instead of the total, one person’s amount instead of the difference, the number sold instead of the number left.

What it looks like

PSLE-style question · 2 marks

Ben and Sam share 60 stickers in the ratio 2 : 3. How many more stickers does Sam get than Ben?

  1. 2 + 3 = 5 units = 60 stickers, so 1 unit = 12
  2. Sam has 3 units = 36. Ben has 2 units = 24.
  3. Sam gets 36 − 24 = 12 more
36 12 ✓

Why 36 is wrong: Sam’s share was written as the answer. The question asked how many more Sam gets than Ben.

Why children do it

  • The last number worked out feels like the answer, whatever the question asked.
  • Multi-step problem sums ask for something a step beyond the obvious quantity, and the final question is read once at the start and then forgotten.
  • Under time pressure, "how many more" and "how many" look the same.

How to fix it at home

  • Have your child underline the question sentence before starting, and read it again before writing the answer line.
  • Ask "what did they actually ask for?" after every word problem at home, before asking whether the answer is right.
  • Write the answer as a sentence: "Sam gets 12 more stickers than Ben." A sentence that repeats the question catches the slip.

Questions parents ask

Is this a careless mistake?

It is a habit, and a fixable one. Children who reread the question before the answer line stop losing these marks within a few weeks.

Does the PSLE give method marks for the right working?

In Paper 2, yes: the working earns its marks even when the final line is wrong. In Paper 1 there is only the answer mark.

How does Knowbotic catch it?

The part-instead-of-whole answer is a known trap on these questions, so the app names the habit and gives more questions until the answer line is right three times in a row.

Where it shows up

Whole numbersFractionsPercentageRatio

Other careless mistakes

Fraction of a remainderMinutes and hours (60, not 100)Percentage of a new totalFound the increase, not the new priceStopped at one part in ratioSimplest form in final fraction answersLeft out the unitsConverting units (kg, ℓ, m, cm³)Collecting like terms in algebraAngle facts (straight line, triangle, quadrilateral)Area, perimeter and volume formulasRadius and diameter in circlesAverage and totalFactors and multiples (HCF, LCM)Calculation slipPlace value and roundingOrder of operationsDecimals: the point and the placesAdding, comparing and dividing fractionsAlgebra: forming, substituting and solvingNumber patterns: the rule and the termReading graphs, tables and scalesNets and solids: faces, edges and vertices

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