1. **State the problem:** Isabelle sells 52 ears of corn out of 80 on Saturday. We want to find how many ears she would sell if the total number of ears was 20 instead of 80. 2. **Understand the concept:** The number of ears sold is proportional to the total number of ears. This means the ratio of ears sold to total ears remains constant. 3. **Set up the proportion:** $$\frac{52}{80} = \frac{x}{20}$$ where $x$ is the number of ears sold when the total is 20. 4. **Solve for $x$:** Multiply both sides by 20: $$x = 20 \times \frac{52}{80}$$ 5. **Simplify the fraction:** $$\frac{52}{80} = \frac{\cancel{52}}{\cancel{80}} = \frac{13}{20}$$ 6. **Calculate $x$:** $$x = 20 \times \frac{13}{20} = \cancel{20} \times \frac{13}{\cancel{20}} = 13$$ 7. **Answer:** Isabelle would sell **13 ears** of corn if the total number of ears was 20.