Stacked discounts do not add up
"20% off, then a further 10%" is not 30% off. The second discount applies to the already-reduced price, so 100 becomes 80 and then 72 — a 28% reduction. The gap widens as the discounts get larger: 50% then 50% is 75% off, not free.
Order does not matter for the final figure, but the wording often implies more than it delivers.
Working backwards from the sale price
To find the original from a discounted price, divide rather than add the percentage back. An item at 80 after 20% off was 100 — that is 80 ÷ 0.8, not 80 + 20%, which gives 96. Adding the percentage back is the most common arithmetic mistake in this area, and it always understates the original.
Frequently asked questions
Is 20% off then 10% off the same as 30% off?
No — it is 28%. The second discount applies to the already-reduced price. The gap grows with larger discounts.
How do I find the original price?
Divide by one minus the discount. An item at 80 after 20% off was 100, not 96 — adding the percentage back gives the wrong answer.
Does tax go on before or after the discount?
After, in almost every jurisdiction — tax is charged on what you actually pay.
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