These three look like three topics but they are one idea: a percentage of a price, either taken off or added on. A discount of 15% leaves 85% of the usual price, so you can reach the price paid in one multiplication. GST in Singapore is 9%, added on, so the total payable is 109% of the ticket price. Simple interest is the same amount every year, always worked out on the money that was put in at the start. The commonest lost mark in this lesson is not arithmetic — it is answering the discount when the question asked for the price paid.
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