Primary 6 · Mathematics
P6 percentage
A discounted price is not the 100%, and the working that assumes it is lands within a few dollars of correct. Here is the pattern, and the question to ask before your child starts.
- Level
- P6
- Usually taught
- Term 1
- Covers
- 2 concepts
What changes at P6
At Primary 6, percentage stops being "find 20% of this" and becomes "find the whole". Most questions now hand your child a part and a percentage, then ask for the amount it came from.
That reverses the arithmetic, and it moves the 100%. Deciding which number in the question is the whole is the actual skill being tested.
The sentence that costs the mark
A bag costs $60 after a 20% discount. What was the original price?
What the working usually does
20% ofthe $60 after=$72
Treats the $60 as the whole, so adds 20% of $60 back on.
What the question asked
20% ofthe original=$75
The $60 is only 80% of the original, so the whole is bigger.
The two answers sit $3 apart and both look sensible for a discounted bag. Nothing in the working looks careless. The question never says which number is the whole, and that is exactly the thing being tested.
The same question, worked properly
Name the whole
the original price = 100%, not the $60This is the step that fails. Every percentage question turns on this line. The $60 is what was paid, not what the bag cost.
Work out what was paid
100% − 20% = 80%, so 80% → $60A 20% discount means 80% of the original was actually handed over.
Find one percent
1% → $60 ÷ 80 = $0.75The MOE unit step, counted in percent instead of parts.
Scale up to the whole
100% → 100 × $0.75 = $75Once 1% is known, every percentage in the question is one multiplication away.
Check it back
20% of $75 = $15, and $75 − $15 = $60The wrong answer fails here. Take 20% off $72 and you get $57.60, which is not the price the question gave.
How can you tell it has clicked?
You do not need to do the maths to check this. When a percentage question is in front of them, ask one thing before they start: "what is the 100% here?"
A child who has understood points at the thing that came first, the original price, the amount before the change. A child who points at the number printed largest in the question is the one who loses these marks.
One thing to try tonight
The next sale sign you walk past, show them the price and ask what it cost before the discount. Not what they would pay. What it was.
It is the same question the exam asks, and it takes twenty seconds. If they reach straight for the number on the tag, that is the habit worth working on.
What your child will meet in this topic
- Percentage Change
- Percent Word Problems
Most Singapore schools introduce this in Term 1, though schools do differ by a term either way. If your child’s school runs a different order, you can set it in the schedule on your dashboard.
What it leads to
Percentage joins ratio and fractions as a third notation for the same split, and P6 word problems happily mix all three in one question.
The "what is the whole" habit is what carries across them. A child who has it reads the mixed questions as familiar. A child who does not meets the same wall three times.
The methods your child will use here
Each one is the same method wherever it turns up, so it is worth learning once.
The same topic in other years
It comes back each year and gets harder, so it helps to see what came before and what is coming.
More in Primary 6
Other topics in the same year, so you can see what sits either side of this one.
Struggling with the working rather than the topic itself? How to help your child with problem sums
See how your child is doing on this topic
StudyLah marks each step separately, so you can see whether it was the setup or the arithmetic that cost the mark.