Answer :

Let's work through the problem step by step to determine what percentage of the veterinarian's patients were small animals.

1. Identify Small Animals:
Small animals in this context include dogs, cats, and ferrets.

2. Count Each Type of Animal:
- Dogs: 7
- Cats: 13
- Horses: 4 (Not considered small animals)
- Ferrets: 3

3. Calculate the Total Number of Animals:
Add up all the animals treated by the veterinarian:
[tex]\[ 7 \text{ (dogs)} + 13 \text{ (cats)} + 4 \text{ (horses)} + 3 \text{ (ferrets)} = 27 \][/tex]

4. Calculate the Number of Small Animals:
Add up the number of dogs, cats, and ferrets:
[tex]\[ 7 \text{ (dogs)} + 13 \text{ (cats)} + 3 \text{ (ferrets)} = 23 \][/tex]

5. Calculate the Percentage of Small Animals:
We use the formula to find the percentage:
[tex]\[ \text{Percentage of small animals} = \left( \frac{\text{Number of small animals}}{\text{Total number of animals}} \right) \times 100 \][/tex]
Substituting the values we have:
[tex]\[ \text{Percentage of small animals} = \left( \frac{23}{27} \right) \times 100 \approx 85.19\% \][/tex]

So, the percentage of the veterinarian's patients that were small animals is approximately 85%. Therefore, the correct answer is:

85%