We know that
There are 20 models in total.
He has three times as many cars as planes.
The first statement can be expressed as
![x+y=20](https://img.qammunity.org/2023/formulas/mathematics/college/edyofv8e0fog2rwzj4fjqxozj0sdhu6kpz.png)
The second statement can be expressed as
![y=3x](https://img.qammunity.org/2023/formulas/mathematics/high-school/x3q8kt3l366jfmm89tfr8zil9wuf8fwkg6.png)
Where y represents cars and x represents planes.
Now, we combine the equations
![\begin{gathered} x+y=20 \\ x+3x=20 \\ 4x=20 \\ x=(20)/(4) \\ x=5 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/re3n1acm10k7ed2saatqmppqv28y27akjz.png)
Then, we find y
![y=3\cdot5=15](https://img.qammunity.org/2023/formulas/mathematics/college/1pchz1achywsq6s6br0sb39qwwdz44wfwf.png)
As you can observe there are three times more cars than planes, which means the ratio is 3:1.