Hi. Technically, if you mix any amount of yellow paint and any amount of blue paint, you will get green paint; it might be a lighter or darker shade of green. If you were to mix equal amounts of true yellow (a primary yellow) and a true blue (a primary blue), then you would get a secondary color of green (a true green). Any other combination other than 50/50 would result in a tertiary color of some shade of green. For example, a bluish green, or. yellowish green. This sounds like more of a math problem though... If you need to end up with 15 cups of a True Green, then you would need equal starting amounts; so 7.5 cups of yellow and 7.5 cups of blue. Sounds like you might be starting with 15 cups of yellow paint(1/2) and 22.5 cups of Blue Paint (3/4) to start. But you would only use 7.5 cups of blue and 7.5 cups of yellow to make 15 cups of green. You would have 7.5 cups of yellow left (1/2) and 22.5-7.5=15, so 15 cups of blue left. Hope this helps.
Eddie
