The ratio of cats to dogs is 4:5.If there are 20 dogs, how many cats are there?
Since the common ratio between cats and dogs is 4:5. We want to know cat and dogs in the ratio x:20. Thus, we can set up the equation as \(\frac{4}{5}=\frac{x}{20}\). Cross multiplication gets us \(80=5x.\) Solving for \(x\) we get that \(\frac{80}{5}=x \to 16=x.\) Now, we know that the number of cats there are is \(\boxed{16}.\)