To estimate the number of orange jelly beans in the bag, we can use the proportion of orange jelly beans drawn in Ava's sample of 20 jelly beans.
In Ava's sample, there were 3 orange jelly beans out of 20 total jelly beans:
\[ \text{Proportion of orange beans} = \frac{\text{Number of orange jelly beans in sample}}{\text{Total jelly beans in sample}} = \frac{3}{20} \]
Next, we'll use this proportion to estimate the total number of orange jelly beans in the bag of 500 jelly beans. We set up the following equation:
\[ \text{Estimated number of orange jelly beans} = \text{Total jelly beans} \times \text{Proportion of orange jelly beans} \]
Substituting in the values:
\[ \text{Estimated number of orange jelly beans} = 500 \times \frac{3}{20} \]
Now, we calculate it:
\[ 500 \times \frac{3}{20} = 500 \times 0.15 = 75 \]
Therefore, the estimated number of orange jelly beans in the bag is:
\[ \boxed{75} \text{ orange jelly beans} \]