The ratio, by definition, is used to compare two quantities.
In this case, according to the information given in the exercise, you know that there are 8 girls and 12 boys in the running club. Therefore, the total number of people in the running club is:
![8+12=20](https://img.qammunity.org/2023/formulas/mathematics/college/60z5ebhg9kgcxf2bw23zbpk9s29mj6z2xq.png)
There are 20 people in the running club.
By definition. a ratio can be written in these forms:
![\begin{gathered} a\colon b \\ \\ (a)/(b) \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/1y6nxxeqqu1n2fcrir9zgtmr8j3cgo5c6e.png)
Then, knowing the explained above, you can determine that the ratio of boys to the total number of runners in the club, is:
![(12)/(20)=(6)/(10)=(3)/(5)](https://img.qammunity.org/2023/formulas/mathematics/college/2ixtjjxbuo1pppjqp7xyi36jbeo6d90aea.png)
Which can be written as:
![3\colon5](https://img.qammunity.org/2023/formulas/mathematics/college/43d0kjk0tethykkliuslyfh1pfwxsyfb2t.png)
Therefore, the answer is:
![3\colon5](https://img.qammunity.org/2023/formulas/mathematics/college/43d0kjk0tethykkliuslyfh1pfwxsyfb2t.png)