G3 Mathematics tuition can help your child reverse a percentage increase by identifying the original value as 100%, expressing the new value as a multiplier of that original, and dividing by the multiplier. After a 20% increase, the new value is 120% of the original: original = new value ÷ 1.20.

For a Punggol parent, the quickest diagnostic question is: ‘Twenty per cent of which amount?’ A child who subtracts 20% of the final price is using a different reference quantity. Start with this explanation before adding more worksheets; the calculation usually becomes clearer once the base is clear.

The 2027 SEC G3 Mathematics syllabus K310 includes reverse percentages. This guide isolates one step within that topic: recovering an original value after an increase. The examples are original teaching exercises, and the school’s current teaching sequence should determine when they are practised.

Confirm the student’s actual subject level and examination year. PG1, PG2 and PG3 are Posting Groups; they do not replace checking each subject’s G level. Ask a provider about subject availability before arranging specialist support.

Imagine a price changing from an unknown amount to $96 after a 20% increase. Ask the student to name the before and after quantities. The unknown original price is the base for the stated increase; the $96 is the result.

Write ‘original: 100%; increase: 20%; final: 120%’. The three labels matter more than a memorised instruction to move the decimal point. They tell the child what the equation represents.

If the child can calculate 20% of $96 but cannot explain why that is the wrong increase amount here, practise reference quantities first. Accuracy with a calculator does not resolve a mistaken model.

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Let the original price be x dollars. Then x + 0.20x = 96, so 1.20x = 96. Dividing gives x = 80. The original price is $80, and the increase is $16.

Check forward: 20% of $80 is $16, and $80 + $16 = $96. This uses the same base as the original statement. The check confirms the interpretation as well as the arithmetic.

The tempting alternative gives $96 − 0.20 × $96 = $76.80. But a 20% increase on $76.80 gives $92.16, not $96. Asking the child to perform this forward check makes the mistaken reference quantity visible.

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A percentage increase and a percentage decrease of the same stated rate generally use different bases when applied consecutively. Multiplying by 1.20 and then by 0.80 gives 0.96, not 1.

To undo multiplication by 1.20, divide by 1.20. The required reduction from the final value is 1 − 1/1.20, or 16⅔%. The student need not calculate this reduction to solve the original problem; it explains why ‘take away 20%’ is not its inverse.

Keep the distinction between subtracting the actual increase and subtracting the stated percentage of the final amount. In the worked example, subtracting the known $16 is correct. The problem is that $16 is not 20% of $96.

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A club’s membership reaches 270 after a 12.5% increase. Write 1.125x = 270, giving x = 240. The increase is 30 members, and 30/240 × 100% = 12.5%.

Now change the question: a price becomes $72 after a 10% decrease. The remaining value is 90% of the original, so x = 72/0.90 = 80. This contrast tests whether the student understands multipliers rather than memorising ‘divide by a number larger than one’.

Use one increase and one decrease with the answers hidden. Ask the student to label the original 100%, form an equation and check forward. A short explanation reveals more than ten unexplained final answers.

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Try this independently: a subscription costs $138 after a 15% increase. What was its original cost? The answer is $120 because 138/1.15 = 120. The increase is $18, which is 15% of $120.

Ask the learner to explain why $138 × 0.85 does not recover the original. A strong response mentions the changed percentage base, not simply that the teacher prefers division.

Continue into the existing percentages and compound-interest guide for wider applications. A tutor can then vary the wording while preserving the same before–multiplier–after structure.

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Use the Primary, PSLE and SEC subject directory to find related questions. Bring one recent piece of work and the teacher’s feedback to a consultation. Ask which step needs repair and how the student will demonstrate progress on a new task.

The Clementi Secondary 1 Mathematics guide illustrates diagnosis, sequenced practice and focused 3-pax teaching. Use these principles when asking how support will fit your child’s actual subject and starting point.

Official reference: SEAB 2027 SEC G3 Mathematics syllabus K310, checked 12 October 2026. The exercises here are original teaching examples, not SEAB examination questions or official model answers.