# RE2 | anthropic/claude-opus-5 | run 1

## Prompt

After a 20% discount, a jacket costs $40. What was the original price? Show your work.

## Response

The original price was **$50**.

## Work

Let \( p \) be the original price. A 20% discount means the customer pays 80% of \( p \):

\[ 0.80p = 40 \]

\[ p = \frac{40}{0.80} = 50 \]

**Check:** 20% of $50 is $10, and \( 50 - 10 = 40 \). ✓

A common mistake is adding 20% to $40 (giving $48), which is wrong because the discount was taken off the *larger* original price, not the sale price.

Want me to show the general formula for reversing any percentage discount?
