Pilar bought a purse on sale for $\$18$, which was one-half of the original price. What was the original price of the purse?

Let $p$ denote the original price. The sale price is one-half of the original, so $18 = \dfrac{1}{2} p$. Multiply both sides by $2$: $36 = p$. Check: half of $\$36$ is $\$18$ ✓. Trap A ($\$9$) takes half of the sale price (going the wrong direction). Trap D ($\$54 = 3 \times 18$) misapplies the relationship.