The ratio of jockeys to trainers is 15 to 18. This is mathematically written as:
[tex]\begin{gathered} 15\colon18 \\ \text{Both 15 \& 18 are factors of }3\text{, hence, we divide through by 3. We have:} \\ \frac{15}{3}\colon\frac{18}{3}\Rightarrow5\colon6 \\ 5\colon6 \end{gathered}[/tex]