When two percentages appear beside a price, adding them may seem natural. In a successive calculation, however, the second percentage applies to an amount that has already changed. A 10% discount followed by another 10% discount therefore does not equal 20% off. All prices here are mathematical illustrations, not a store, credit or service offer.
Identify the base for each step
A percentage alone does not describe the calculation. Start by asking what amount it refers to. The first discount may use the original price, while the second uses the reduced one. If an offer does not explain its method, ask for clarification. The same wording does not necessarily mean identical promotion rules everywhere.
Calculate two 10% reductions
Begin with 100 manat. The first 10% discount removes 10 manat, leaving 90. The next 10% is calculated from 90, so it removes 9. The final price is 81 manat: a total reduction of 19 manat, or 19% of the original amount. A compact check is 100 × 0.9 × 0.9.
Different percentages follow the same principle
For an illustrative 200 manat price, a 20% discount leaves 160. A further 5% removes 8 manat, leaving 152. The difference from the original is 48 manat, making the combined reduction 24%. Adding 20 and 5 gives 25%, but ignores the changed base for the second calculation.
An increase may not restore the old price
Reducing 100 manat by 10% gives 90. Increasing 90 by 10% adds 9, producing 99. To bring 90 back to 100, divide the required increase of 10 by the new base of 90: approximately 11.11%. A reduction and its reversal use different starting amounts.
Avoid rounding too early
Rounding every intermediate step to a whole manat can change the final result. Retain precision during calculations and state how the displayed amount is rounded. The seller's actual pricing rules and extra services must be checked separately; a simple percentage illustration does not describe the entire invoice.
Use a short checking table
Record the original price, first operation, new base, second operation and final amount on separate rows. Divide the total difference by the original price and multiply by 100. This shows what you actually pay alongside the percentage highlighted on screen.
When applying examples from OLAI, clarify what each input means first. A small manual check can also reveal incorrect starting information.
The cover is an AI-generated illustration.