Final answer:
To keep a constant rate of proportionality, you would need to add 9/4 cups of yellow paint.
Step-by-step explanation:
To keep a constant rate of proportionality, we need to determine how many cups of yellow paint would need to be added if 4 cups of red paint are added to the mixture. In the original mixture, the ratio of red paint to yellow paint is 1/3 cups to 3/4 cups. We can set up a proportion to solve for the cups of yellow paint:
1/3 cups / 3/4 cups = 4 cups / x cups
Cross multiplying, we get:
(1/3) * x = (3/4) * 4
Simplifying, we find that:
x = (3/4) * 4 / (1/3)
x = 9/4
Therefore, the amount of yellow paint that would need to be added to keep a constant rate of proportionality is 9/4 cups.