A veterinarian treated 7 dogs, 13 cats, 4 horses, and 3 ferrets. What percentage of his patients were small animals?

According to your definition, horses are the only creatures labeled as "not small". To determine the percentage, divide the number of small animals by the total number.

So, 7 dogs + 13 cats + 3 ferrets = 23 small animals

7 dogs + 13 cats + 3 ferrets + 4 horses = 27 total animals.

Thus,

The multiplication by 100 is necessary because dividing results in a decimal, and a percentage is a fraction of 100.

This leads us to the calculation which yields

85.18%