Question: By selling a sofa for $\usd{}408$, a retailer suffers a loss of $4\%$. Find the cost price of the sofa.

Step 1. Anchor the percentages: the loss is $4\%$ of the cost price, so the cost price is the $100\%$.

Selling price $= 100\% - 4\% = 96\%$ of the cost price.

Step 2. Write what is known against its percentage:

Step 3. Scale to $1\%$, then to $100\%$ (the unitary method):

Step 4. Or in one line: $\text{cost} = \dfrac{408}{0.96} = \usd{}425$.

Check. $4\%$ of $425$ is $17$, and $425 - 17 = 408$. ✓

The same one-liner handles discounts and GST questions: price after +9% GST ÷ 1.09 recovers the pre-GST price.

⚠ Watch out: The trap answer is $408 \times 1.04 = \usd{}424.32$ — adding $4\%$ of the selling price. Wrong, because the $4\%$ was a slice of the original, which is bigger. Whenever the original is unknown, divide by the multiplier ($0.96$); never multiply the changed value back up.

Question: In a sale, a table cloth's original price of $\usd{}33.25$ was reduced by $20\%$. On the last day there was a further $30\%$ off the sale price. How much did Sharon pay?

Step 1. First reduction — paying $100\% - 20\% = 80\%$:

Step 2. Second reduction acts on the new price, not the original: $100\% - 30\% = 70\%$:

Step 3. Same answer as one combined multiplier:

Step 4. Notice what the combined multiplier says: two successive discounts of $20\%$ and $30\%$ leave $56\%$ — an overall discount of $44\%$, not $50\%$.

⚠ Watch out: Successive percentages never simply add — each one acts on the running value. Chain the multipliers ($\times 0.8 \times 0.7$) and the arithmetic stays honest; the same chaining handles successive increases ($\times 1.15$, etc.) and mixed cases.