Let's denote the number of planes that Jamaal has as \( p \). According to the problem, the number of cars he has is three times the number of planes, which means he has \( 3p \) cars.
Since the total number of models (planes and cars) is 20, we can set up the equation:
\[ p + 3p = 20 \]
This simplifies to:
\[ 4p = 20 \]
Now, dividing both sides by 4:
\[ p = 5 \]
So, Jamaal has 5 planes. To find the number of cars:
\[ 3p = 3 \times 5 = 15 \]
Now, Jamaal has 15 cars.
Next, we need to find the ratio of the number of cars to the total number of models. The total number of models is:
\[ p + 3p = 20 \]
The ratio of the number of cars (15) to the total number of models (20) is:
\[ \text{Ratio} = \frac{\text{Number of Cars}}{\text{Total Models}} = \frac{15}{20} \]
This can be simplified by dividing both the numerator and the denominator by 5:
\[ \frac{15}{20} = \frac{3}{4} \]
Thus, the ratio of his cars to total models is \( 3:4 \).
So, the answer is:
3:4