Final answer:
To represent 4/5 on a model where the fully shaded portion represents 100%, you would shade 80% of the model.
Step-by-step explanation:
If a fully shaded model represents 100%, then a model shaded to represent 4/5 would be equivalent to shading 80% of that model. Since there are five equal parts in a whole (1), representing 100%, each part is equivalent to 20% (100% divided by 5). To represent 4/5, you would shade four of these parts, which amounts to 4 parts × 20% per part = 80% of the model shaded.