Discounts and increases
- 25% off 800,000 Toman: 800,000 × 0.75 = 600,000 Toman.
- A 10% increase means multiplying by 1.10.
Two discounts don't add up
A 20% discount followed by another 10% is not 30% off. The second discount applies to the already-reduced price: 0.80 × 0.90 = 0.72, so the total discount is 28%.
Reversing a percentage
If a price is 330,000 Toman after a 10% increase, the original price is 330,000 ÷ 1.10 = 300,000 Toman — not 330,000 minus 10%.
Percent vs. percentage points
If a rate rises from 12% to 15%, it has risen by 3 percentage points, which is a 25% increase in the rate itself (3 ÷ 12). News reports often mix these up.
Quick mental tricks
- 10% of a number: move the decimal point one place left.
- 5% is half of 10%; 15% is 10% plus 5%.
- x% of y equals y% of x: 8% of 50 is the same as 50% of 8, which is 4.
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Asaiejadoo — everyday calculation and AI guides, part of the ZIBADIS network founded by Masoud Moghaddam in Tehran.
