1/2 of the children within the city limits have a dog, 1/3 have a cat, and 1/6 have a dog and a cat. What fraction of those who have a dog also have a cat?

It is 1/6 because it says that in the problem that "1/6 people have a dog and a cat" and it is asking "What fraction of those who have a dog also have a cat?" It says the answer in the problem