Comprehensive Calculator Guide
To reduce a number by a percentage, multiply it by (1 − rate ÷ 100). A SAR 450 item with 30% off costs 450 × 0.70 = SAR 315, a saving of SAR 135. It works backwards too: enter the reduced price and the rate to get the original, or both values to get the rate.
How a percentage decrease works
The amount off is value × rate ÷ 100; the new value is what is left. Multiply by the factor for speed: 0.70 for 30% off, 0.95 for a 5% drop. To recover the original, divide by the factor: SAR 240 after 20% off was 240 ÷ 0.80 = SAR 300, not 288.
A cut followed by a rise of the same rate does not return you to the start: 450 down 30% is 315, and 315 up 30% is only 409.5. Recovering from a 30% fall takes a 42.86% rise.
How to Use
- 01Enter the original value and the rate to get the reduced value and the amount off.
- 02To find the original, enter the reduced value and the rate.
- 03To find the rate, enter both values. Rates run from 0 to 100.
Formula Used
New value = value × (1 − rate ÷ 100) | Original = new value ÷ (1 − rate ÷ 100)Practical Examples
Example 1: a shop discount
SAR 450 with 30% off: SAR 315, saving SAR 135.
Example 2: weight down 5%
90 kg down 5%: 85.5 kg.
Example 3: price before a discount
SAR 240 after 20% off: originally SAR 300.
Important Tips
- Two discounts of 20% then 10% make 28%, not 30%.
- Compare offers by their final price, not their rates.
Common Mistakes to Avoid
- Adding the rate back to the reduced price to find the original.
- Expecting an equal percentage rise to undo a fall.
Frequently Asked Questions
- How do I take 25% off a price?
- Multiply by 0.75: SAR 400 becomes SAR 300.
- How do I find the decrease between two numbers?
- Divide the drop by the old value and multiply by 100: 500 to 400 is 20%.
- How do I find the price before a discount?
- Divide by (1 − rate ÷ 100): 315 after 30% off was 450.
- Does 50% off twice make it free?
- No, it leaves a quarter of the price, a 75% total discount.