Your child can calculate 25% of a number. Then a question gives the price after a discount, and the same calculation no longer answers it. Before choosing an operation, ask: “Which amount represents 100%?”
That amount is the reference for the percentage. Naming it helps you distinguish the original amount, the change and the amount left. The examples below are invented practice questions, with prices in Singapore dollars. They are not real offers or examination questions. Use them when your child has already met percentages in class.
Start with a sentence, then attach the percentage
In “25% of the original price”, the original price represents 100%. The discount is one quarter of that price. A 25% discount leaves 75% of the original price to pay.
The OpenStax reference on percentage applications describes the amount a percentage is taken of as the base. It also calculates a percentage increase or decrease relative to the original amount. The worked situations and parent prompts here are our own examples.
Try completing this sentence before doing any arithmetic: “The percentage is taken of ______.” Write the quantity in words, such as “the price before the discount”. You may know what the quantity means even when its value is still unknown.
1. Find the price after a discount
Practice question: A backpack costs $84 before a 25% discount. What is the price after the discount?
Here, 100% is the original $84. Work out the discount first: one quarter of $84 is $21. Then subtract it: $84 − $21 = $63.
| Quantity | Percentage of original price | Amount |
|---|---|---|
| Original price | 100% | $84 |
| Discount | 25% | $21 |
| Price to pay | 75% | $63 |
You can also calculate 75% of $84 directly: 0.75 × $84 = $63. Both routes describe the same situation. If your child answers $21, ask, “What does $21 describe?” The calculation has found the discount, but the question asks for the price to pay.
2. Find the original price when the discounted price is given
Changed question: A backpack costs $63 after a 25% discount. What was its original price?
The original price still represents 100%, but this time we do not know its value. The $63 represents the 75% remaining. Write that relationship before calculating:
- 75% of the original price = $63.
- 1% of the original price = $63 ÷ 75 = $0.84.
- 100% of the original price = $0.84 × 100 = $84.
If your child uses decimal multipliers, the same relationship is 0.75 × original price = $63, so the original price is $63 ÷ 0.75 = $84. Use the representation they understand and have been taught.
Why not simply add 25% to $63? That takes 25% of the discounted price: $15.75. Adding it gives $78.75, which uses the wrong reference amount. The original discount was $21, because it was 25% of $84.
Check by going forwards: 25% of $84 is $21, and $84 − $21 returns the given $63. Just checking that the original price is larger is not enough; an incorrect answer can also be larger.
3. Recheck the base when a second change happens
Suppose a fictional item's price falls by 20% from $50, then rises by 20% of its reduced price. Does it return to $50?
- First change: 20% of $50 is $10. The reduced price is $40.
- Second change: 20% of $40 is $8. The new price is $48.
The percentage number is the same, but the reference amounts are different. The second change uses $40 as its 100%. A $10 decrease followed by an $8 increase does not cancel out.
Do not carry the first 100% label through every later step automatically. Read what the second percentage is taken of. If a question explicitly refers back to the original amount, use that original amount instead.
Try two questions with the same given amount
For each question, first write what represents 100% and what percentage the given $72 represents. Then solve it.
- A bag costs $72 before a 25% discount. Find the price after the discount.
- A bag costs $72 after a 20% discount. Find the original price.
Open the worked answers
- The original price is 100% = $72. The price after the discount is 75% of $72: 0.75 × $72 = $54. The $18 discount and $54 remaining add to $72.
- The original price is 100%, with an unknown value. The given $72 is 80% of it. So 1% = $72 ÷ 80 = $0.90, and 100% = $90. Check: 20% of $90 is $18, and $90 − $18 = $72.
A useful prompt for the next homework session
Choose one percentage question and ask your child to label the quantities before calculating. If they cannot identify the reference amount, return to the sentence that describes the relationship. Saying “multiply” or “divide” immediately supplies a step without showing why it fits.
Once they have an answer, ask them to explain what it means and check it against the original question. Our guide to three ways to check a Math answer gives further examples. For help without taking over the solution, try one hint at a time.
If you are exploring additional support, browse Genie's Math programmes and choose the level relevant to your child.
Source note: Reviewed on 23 October 2026. OpenStax was used to check the mathematical definitions. The practice questions and parent prompts are Genie's own suggestions, not an official examination method or a statement about a particular year's syllabus.