Common P5-P6 maths mistakes before bigger exams

Common P5-P6 maths mistakes before bigger exams

When reviewing P5–P6 work, check reading, method choice, calculation and the final answer separately. Grouping similar mistakes can help you choose a focused next task. The examples below distinguish P5 percentage work from P6 ratio work.

The mistakes that feel small but cost a lot

Check whether a mental shortcut hides the working, whether the method fits, and whether the final answer addresses the question.

Missing working can make an error harder to trace. Ask the child to show intermediate steps before deciding where the misunderstanding began.

Why revision often stays too general

Some children do paper after paper without understanding which types of mistakes are repeating. That makes revision feel busy but not especially corrective.

Group observed errors by reading, method choice, calculation or incomplete working. Use those observations to choose a specific practice focus.

How guided review helps families and centres

This is where guided revision tools matter. Children need help analysing what happened, not only hearing that they should be more careful next time.

Zairoo offers topic-based practice and step-by-step question guidance. Families can keep a short record of the mistakes they observe to choose a practice focus.

Primary 5 example: distinguish the discount from the sale price

A bag costs 120 dollars before a 15% discount. Find the sale price. The whole is the original price, 120 dollars.

1. 1% is 120 ÷ 100 = 1.20 dollars.
2. 15% is 1.20 × 15 = 18 dollars. This is the saving.
3. Sale price: 120 − 18 = 102 dollars, equivalent to 85% of the original price.

Try an item priced at 90 dollars with a 20% discount. The saving is 18 dollars and the sale price is 72 dollars. Continue with the Primary 5 percentage guide.

Primary 6 starting example: count the total ratio parts

The ratio of red counters to blue counters is 2 : 3. There are 30 counters altogether. How many are blue? A common error is to divide 30 by 3, even though 30 represents both colours.

1. Total parts: 2 + 3 = 5.
2. One part: 30 ÷ 5 = 6 counters.
3. Blue counters: 3 × 6 = 18. Red counters: 2 × 6 = 12. Check: 18 + 12 = 30.

Try a new example: keep the ratio 2 : 3 but use 40 counters altogether. There are 24 blue and 16 red counters. Ask your child to label what each part represents before calculating.

Continue with the Primary 6 ratio guide, or choose free Primary 1–6 worksheets for a short practice session.

Primary 6 next step: three-part ratios and fractions of the whole

Red, blue and green counters are in the ratio 2 : 3 : 4. There are 72 counters altogether. How many are blue, and what fraction of all the counters are blue?

1. Total parts: 2 + 3 + 4 = 9.
2. One part: 72 ÷ 9 = 8 counters.
3. Blue: 3 × 8 = 24 counters.
4. Blue as a fraction of the whole: 3/9 = 1/3. Check: 16 red + 24 blue + 32 green = 72.

Try the same ratio with 90 counters altogether. There are 30 blue counters, and the blue fraction is still 1/3. The full counts are 20 red, 30 blue and 40 green. Ask why the total changes but the ratio and fraction do not.

Primary 5 fractions: check regrouping before subtracting

For 4 1/4 − 1 2/3, first express the fraction parts in twelfths: 4 3/12 − 1 8/12. There are too few twelfths in the first fraction part, so regroup one whole: 4 3/12 = 3 15/12. Now subtract to get 2 7/12. Check by adding 1 2/3 to 2 7/12: the result is 4 1/4.

Try 3 1/6 − 1 3/4 next. Use twelfths and regroup: 3 2/12 = 2 14/12, so the difference is 1 5/12. The Primary 5 fractions guide covers mixed-number operations, fraction-to-decimal conversion and multiplication. Choose the section that matches the observed error.

Primary 5 rate: match the unit before dividing

A tap supplies 90 litres in 1 hour 30 minutes. To find litres per minute, convert the whole duration first: 1 hour 30 minutes = 90 minutes. The rate is 90 ÷ 90 = 1 litre per minute. Dividing by 1.30 would treat a clock-style notation as a decimal number of hours and would not answer the question.

For a fresh attempt, a tap supplies 120 litres in 1 hour 20 minutes. That is 80 minutes, so the rate is 120 ÷ 80 = 1.5 litres per minute. Check: 1.5 × 80 = 120 litres. Use the Primary 5 rate guide to connect the amount, the number of units and the amount per unit.

Sources and example notes

Singapore topic levels are referenced to the MOE Primary Mathematics syllabus (October 2025). Upper-primary level labels here follow the Standard syllabus. These original examples practise selected skills; they are not official exam questions or a complete assessment.

The EEF’s Key Stages 2 and 3 guidance, recommendation 1, supports using children’s responses to plan further teaching. It concerns ages 7–14 in England, not Singapore topic placement or evidence about Zairoo’s results.

What parents should do next

At your next revision session, do not only ask how many questions were done. Ask what type of mistake appeared most often.

Use the observed mistake to choose the next practice set, and check the reasoning again on a different question.

Want more support? Start with Zairoo’s free Basic plan for Singapore Primary 1–6 maths practice and step-by-step question guidance. Basic has usage limits. See the current plans and limits to compare Basic and Premium.