10 Most Common PSLE Maths Mistakes (And How to Fix Them)
Every year, PSLE maths trips up students in the same ways. These are not difficult concepts — they are patterns of error that repeat across thousands of papers. If your child can learn to spot these traps, they can pick up marks that others leave on the table.
Here are the 10 most common PSLE maths mistakes we see, drawn from real student errors analysed by Lion City Scholar.
1. Misreading "How Many More" vs "How Many"
The question asks "How many more apples does Ali have than Bala?" and the student gives the total number of apples Ali has.
Why it happens: Students scan the question too quickly and miss the comparison word. Their brain sees "how many" and stops reading. Fix: Train your child to underline the key phrase before solving. Circle "more than", "less than", "difference", "left".2. Forgetting to Convert Units
A question gives length in metres and asks for the answer in centimetres. The student solves the maths correctly but leaves the answer in metres.
Why it happens: The calculation feels like the hard part, so once it is done, the student feels finished. The unit conversion is an afterthought. Fix: Write the required unit next to the answer blank before starting the calculation. This makes it impossible to forget.3. Fraction of a Remainder Errors
"Ali spent 1/3 of his money on a book. He spent 1/4 of the remainder on a pen. How much did he have left?"Students often take 1/4 of the original amount instead of 1/4 of the remainder.
Why it happens: The word "remainder" is easy to miss, especially under time pressure. Fix: Draw a simple bar model. Shade the first fraction, then clearly mark what is left before taking the second fraction from it.4. Not Answering What the Question Asks
The question asks for the cost of 3 items. The student correctly finds the cost of 1 item and writes that as the answer.
Why it happens: The student feels relief after cracking the hard part and rushes to write the answer without re-reading the question. Fix: After solving, re-read the last sentence of the question. Does your answer match exactly what was asked?5. Percentage Increase vs Percentage Of
"The price increased by 20%." Students calculate 20% of the new price instead of 20% of the original price. Why it happens: Percentage questions require careful tracking of which number the percentage applies to. Under pressure, students grab the nearest number. Fix: Always label your working: "20% of original = ..." Writing it out forces clarity.6. Equal Parts Assumption in Ratio
A ratio question gives A:B = 2:3 and B:C = 4:5. Students cannot combine them because B has different units (3 vs 4).
Why it happens: Students try to write A:B:C = 2:3:5, not realising B must be the same value in both ratios. Fix: Find the LCM of B (LCM of 3 and 4 = 12). Scale both ratios so B = 12. Then A:B:C = 8:12:15.7. Forgetting to Account for "Both" in Overlap Problems
"12 students play football, 8 play basketball, and 5 play both." When asked how many play at least one sport, students add 12 + 8 = 20 instead of 12 + 8 - 5 = 15. Why it happens: The word "both" signals overlap, but students default to addition. Fix: Draw a simple Venn diagram every time you see "both" or "also" in a question.8. Rounding Too Early
In multi-step calculations, students round intermediate answers (e.g. 3.333 becomes 3.33) and the final answer drifts.
Why it happens: Students are taught to give neat decimal answers, so they round at every step. Fix: Keep full decimal values in working. Only round the final answer, and only if the question asks you to.9. Speed-Distance-Time Formula Mix-Up
Students confuse distance = speed × time with speed = distance × time.
Why it happens: Three variables, three formulas. Under pressure, the wrong one surfaces. Fix: Remember the triangle: D on top, S and T on the bottom. Cover what you want to find — the remaining two show the formula.10. Leaving Out the Statement in Word Problems
The student does all the maths correctly but does not write a final statement. In PSLE, this can cost 1 mark per question.
Why it happens: The student sees the correct number and assumes the job is done. Fix: Always end with a sentence: "Ali has 24 apples left." Practise this in every homework until it becomes automatic.What Parents Can Do
You do not need to be a maths expert. You just need to help your child see their patterns. When the same type of mistake keeps appearing, that is the one to focus on.
This is exactly what Lion City Scholar does — it tracks your child's mistakes over time and uses AI to spot the patterns. Instead of going through stacks of old papers, your child can review their weak spots in minutes.
Every mistake is a chance to learn. The key is making sure it does not get forgotten.