PSLE Maths Percentage: Discount, GST & Percentage Change

📅 Published: August 2026 · ✍️ By: PSLE Hero Editorial Team

Percentage is one of the most consistently tested topics in Primary 5 and Primary 6 Mathematics. Appearing across Paper 1 (mental and non-calculator arithmetic) and Paper 2 (structured multi-step word problems), mastering percentage change, discount, GST, and remainder percentage problems is key to securing top AL grades.

📖 Related Maths Revision Guides:

• PSLE Maths Revision & Exam Tips (General paper strategy & timing)
• PSLE Maths Heuristics Guide (5 core heuristic types)
• PSLE Maths Model Drawing Guide (Part-Whole & Comparison models)
• PSLE Maths Fractions Guide (Remainder concept & equal fractions)
• PSLE Maths Ratio Guide (4 core ratio problem types)

1. The 4 Most Common Percentage Traps in PSLE Maths

Most marks lost in percentage problem sums stem from misidentifying the base quantity (the "100%") or applying percentage operations in reverse.

Trap 1: Confusing "Percentage Of" with "Percentage More/Less Than"

"20% of $50" equals $10. But "20% more than $50" means $50 + $10 = $60 (or 120% of $50). Always look out for the phrasing "more than" or "less than" to determine whether to add/subtract from 100%.

Trap 2: Reversing Percentage Change Incorrectly

If a price increased by 20% to $120, students often try to find the original by subtracting 20% of $120 ($24), arriving at $96 (wrong!). The correct base is the original amount (100%): 120% = $120, so 100% = $100.

Trap 3: Applying GST to the Original Price Instead of Discounted Price

In Singapore real-world and exam contexts, GST is calculated on the final selling price after discount, not before the discount. Always compute the discounted price first, then apply GST to that amount.

Trap 4: Percentage Point Change vs Percentage Change

If test scores rise from 60% to 75%, the increase is 15 percentage points, but the percentage increase is (15 ÷ 60) × 100% = 25%. PSLE questions test percentage change relative to the initial value.

2. Core Concept 1 — Percentage Change (Increase & Decrease)

Percentage change measures how much a quantity has grown or shrunk relative to its original starting value. Formula: Percentage Change = (Change ÷ Original Amount) × 100%.

Worked Example: Percentage Increase

A school canteen raised the price of a bowl of noodles from $1.80 to $2.25. What was the percentage increase in price?

Step 1: Find the absolute change in price.
Increase = $2.25 − $1.80 = $0.45.

Step 2: Divide by original price and convert to percentage.
Percentage increase = ($0.45 ÷ $1.80) × 100% = 0.25 × 100% = 25%.

3. Core Concept 2 — Discount & GST Problems

Discount reduces the cost price to the selling price: Selling Price = Original Price × (100% − Discount%). GST adds tax to the selling price: Final Price = Selling Price × (100% + GST%).

Worked Example: Discount and GST

A school bag is listed at $120. During a sale, it is offered at a 15% discount. A 9% GST is then added to the discounted price. How much does a customer pay in total?

Step 1: Calculate the discounted selling price (85% of original).
Selling Price = $120 × (100% − 15%) = $120 × 0.85 = $102.

Step 2: Add 9% GST to the discounted price.
Final Amount = $102 × (100% + 9%) = $102 × 1.09 = $111.18.

4. Core Concept 3 — Multi-Step Percentage Word Problems (Remainder Method)

In P6 Paper 2, percentage questions often involve spending a portion of a remainder. Just like fraction remainder problems, break down the whole step by step.

Worked Example: Percentage Remainder Problem

Priya spent 30% of her money on books and 20% of the remainder on stationery. She had $280 left. How much money did she have at first?

Step 1: Find the remainder percentage after books.
Remainder = 100% − 30% = 70% of total money.

Step 2: Find percentage spent on stationery relative to total.
Stationery = 20% of 70% = 0.20 × 70% = 14% of total money.

Step 3: Find percentage of total money left.
Money left = 100% − 30% − 14% = 56% of total money.

Step 4: Solve for 100% (original total).
56% of total = $280
1% of total = $280 ÷ 56 = $5
100% (Original) = 100 × $5 = $500.

5. Parent Checklist for Home Practice

Use this 5-point checklist when going through percentage corrections with your child:

Identify the 100% base: Always check what quantity represents the 100% starting point before applying any percentage calculation.
Underline trigger words: Circle words like "more than", "less than", "remainder", "discount", and "GST".
Express percentage changes as multipliers: A 20% increase is 1.20× original; a 15% discount is 0.85× original.
Never subtract percentages directly in reverse problems: If 120% = $120, divide by 1.20 to find 100%. Do not subtract 20% from $120.
Check GST sequence: Ensure GST is applied after the discount is subtracted, not before.

Practise PSLE Maths Questions on PSLE Hero

Master percentage word problems, discount & GST calculations, and remainder concepts with targeted practice questions designed for Singapore primary students.

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Frequently Asked Questions

Q: Is GST tested in the 2026 PSLE Maths exam?

Yes. GST (Goods and Services Tax) word problems appear in PSLE Maths Paper 2. In Singapore, GST is applied to the price after any discount has been deducted. Students should know how to calculate final price = discounted price × (1 + GST rate).

Q: What is the difference between a percentage point change and a percentage change?

A percentage point change is the arithmetic difference between two percentages (e.g. from 60% to 75% is a 15 percentage point rise). A percentage change expresses this difference as a proportion of the original percentage (15 ÷ 60 × 100% = 25% increase). PSLE questions typically ask for percentage change.

Q: How do I help my child reverse a percentage increase without making common mistakes?

Teach your child that if a price rises by 20%, the new price is 120% of the original. To find the original, divide the new price by 1.20 (for a 20% increase) or by 0.85 (for a 15% discount). Never subtract the percentage directly from the new price.