Final answer:
We can infer that about 80% of dog owners clean up after their dog based on the study.
Step-by-step explanation:
To determine the percentage of people who clean up after their dog while walking on public trails, we can use the data collected by the runner. Out of 20 dog owners observed, 4 did not clean up after their dog. To find the percentage, we divide the number of dog owners who clean up by the total number of dog owners and multiply by 100. Therefore, the percentage of dog owners who clean up after their dog is (20-4)/20 * 100 = 80%. From this study, we can infer that about 80% of dog owners clean up after their dog.