A discount means you pay less than 100 percent. GST means you pay more than 100 percent. Every time, ask which price the 100 percent belongs to. That's the price the percentage is worked out on. In the lesson. Every time, ask which price the one hundred percent belongs to. That's the price the percentage is worked out on.
Lesson video, with the working
Discount and GST questions
3 min 54 s
The film teaches 2 questions in turn. Each question shows first; its working is written as the film explains it.
A television has an original price of $500. The shop gives a 20% discount, and then 9% GST is added to the discounted price. How much does the customer pay?
The customer pays $436.
Ans: $436
Example 1
A fan is sold at 20% off. After the discount it costs $240. What was the original price?
The fan was priced at $300.
Ans: $300
How to solve it
Draw the original price, 500 dollars, as one bar. It is the whole, so it is 100 percent.
A 20 percent discount comes off, so the customer pays 100 percent minus 20 percent, which is 80 percent.
Find 80 percent: 1 percent is 500 dollars shared into 100, which is 5 dollars, so 80 percent is 400 dollars.
GST is worked out on the discounted price. Now 400 dollars is the new 100 percent, and 9 percent is added, making 109 percent.
Find 109 percent: 1 percent is 4 dollars, so 109 times 4 is 436 dollars.
A discount means you pay less than 100 percent. GST means you pay more than 100 percent. Every time, ask which price the 100 percent belongs to. That's the price the percentage is worked out on.
Practice questions with worked solutions
Question 1 is free to try. The other 5 open in the free trial, each with its full working.
How do you solve discount and GST questions in P6?
Discount and GST were first taught a year earlier.
What your child learns here
Discount and GST were first taught a year earlier. In Primary 6 they come back in longer word problems, often run backwards from the amount paid. Your child learns that each percentage belongs to its own whole: the discount to the original price, the GST to the discounted price.
Find a discount and the price after the discount.
Add GST to a price, working on the price after any discount.
Work backwards from an amount paid to the original price, one whole at a time.
Apply percentage rates that only apply to part of an amount, such as complete blocks or hours after a limit.
Does the answer make sense?
A discount must make a price smaller, and adding 9% GST raises a price by less than a tenth. So your child's 9-hour repair bill sits just above the charge before GST, and a fridge bought at 25% off with GST added must have had an original price above what was paid.
How to practise these questions
The practice set on this page is all Challenge questions, which work backwards through a discount and GST on different wholes, combine two items or two rates, or apply a discount only to complete groups. If discount and GST questions feel tangled, read the written step-by-step solution.
Questions parents ask
What GST rate do these questions use? Each question states the rate it uses. Singapore's GST is 9% at the time of writing, and the worked example on this page uses 9%.
Is GST added before or after the discount? After. The discount comes off the original price first, and GST is worked out on the price after the discount.
Are discount and GST in the P6 syllabus? Finding discount, GST and annual interest is taught the year before Primary 6. In Primary 6 these questions can run backwards from the amount paid, which uses the P6 outcome of finding the whole given a part and the percentage.
