Yellow:blue is a ratio of 2:3, meaning that 2/5 of the desired mixture is yellow. From this, you need to find how much yellow is necessary for 20 ounces. Well, 2/5 of the 20 ounces will be yellow paint, while the other 3/5 will be blue. Therefore:
\(\frac{2}{5} * 20 = \frac{40}{5} = 8\)
So she will need 8 ounces of yellow paint to get 20 ounces of the desired mixture. Hope this helps! :)
