WebToolArcFormula and interpretation
original price = sale price ÷ (1 − discount rate).
A 100% discount has no finite reverse original-price solution.
Worked check
If a sale price is $80 after a 20% discount, the retained fraction is 0.80, so the original price is 80 ÷ 0.80 = $100. A 100% discount cannot be reversed to one finite original price because the retained fraction is zero.
Rule: original price = sale price ÷ (1 − discount rate). A 100% discount has no finite reverse original-price solution. For a final check, estimate the expected size of the answer before copying it, keep units consistent, and round only the displayed result rather than intermediate values. Re-enter one simple case by hand when possible; a result with the wrong sign or order of magnitude usually points to an input or reference-base mistake.