One discount or two
0 gives $56.00. 20 gives $44.80 — a difference of $11.20 less (-20.0%).
The same 30%-off ticket, with and without the extra sign.
| Input | 0 | 20 |
|---|---|---|
| Original price(USD) | 80 | 80 |
| Discount(percent) | 30 | 30 |
| Extra discount on the sale price(percent) | 0 | 20 |
| Sales tax(percent) | 0 | 0 |
| Final price | $56.00 | $44.80 |
Every figure, both ways
| Step | 0 | 20 | Difference |
|---|---|---|---|
| First discount | 24 | 24 | 0 |
| Price after the first discount | 56 | 56 | 0 |
| Extra discount, taken off the sale price | 0 | 11.2 | +11.2 |
| Price after both discounts | 56 | 44.8 | -11.2 |
| You save | 24 | 35.2 | +11.2 |
| Effective discount(%) | 30 | 44 | +14 |
| Sales tax on the discounted price | 0 | 0 | 0 |
| Total to pay | 56 | 44.8 | -11.2 |
Questions people actually ask
- Does lowering extra discount on the sale price change the answer in proportion?
- The two sides differ by 20.0% in the answer. Read the step table below to see which line moves and which does not — that is where a formula stops being a black box.
- What is held constant between the two columns?
- Everything except extra discount on the sale price: original price, discount, sales tax. That is what makes the difference attributable — change two things at once and neither column tells you which one moved the answer.
- Can I compare my own two numbers?
- Yes, from the address bar: add ?a.extra=… and &b.extra=… to set each side, and a parameter without a prefix sets both at once. The page is computed per request, so any pair works — these two are only the ones worth a link.
Change either side by adding query parameters — ?a.extra=… and b.extra=…. A parameter without a prefix sets both sides at once. Source: NIST Handbook 130 — Uniform Regulation for the Method of Sale of Commodities