How to calculate percent off — “X% off” step by step (Grade 7)
“X% off” means a percentage reduction on a price. The saving is price · X ÷ 100, and you pay the remaining factor (1 − X ÷ 100) of the price. Worked example: 30% off $120 → $36 saved, $84 to pay. Suitable for Grade 7 / Year 8 percentages.
Quick answer
At X% off, you save price · X ÷ 100 and pay the rest. Example: 30% off $120 is 120 · 30 ÷ 100 = $36 saved, so you pay $84. If you only know the price paid, recover the original with paid ÷ (1 − X ÷ 100).
At a glance
| Example | 30% of $120 |
|---|---|
| Method | Saving = price · X ÷ 100 |
| Steps | 3 |
| Result | $36 saved, $84 to pay |
| Reverse | 84 ÷ 0.7 = $120 |
| Grade level | Grade 7 (ages 12–13) |
Worked example: 30% off $120
We compute the saving first, then subtract it from the price.
How to calculate a percent discount
These steps work for any discount of the form “X% off”.
Step 1 · Start
30% of $120Given: $120 price, 30% off.Step 2 · · %
120 · 30 ÷ 100Price times the rate, divided by 100.Step 3 · Saving
= $36That is how much you save.Step 4 · Amount due
120 − 36 = $84Subtract the saving from the price — that is what you pay.
Why the discount formula works
An X% discount takes exactly that share off the price, namely price · X ÷ 100. What remains is the remaining factor (1 − X ÷ 100): at 30% off you pay 70% of the price, so the factor is 0.7. Because the price paid is (1 − X ÷ 100) of the original, you get back to the original by dividing — not by adding the discount on again, since the percentages refer to different bases.