The teaspoons of red paint needed to mix with 15 teaspoons of blue paint is 5 teaspoons.
How much red paint would you need?
Mixture A:
Red paint = 3 teaspoons
Blue paint = 9 teaspoons
Mixture B:
Red paint = x teaspoons
Blue paint = 15 teaspoons
Set the proportion
3 : 9 = x : 15
3/9 = x/15
cross product
3 × 15 = 9 × x
45 = 9x
Divide both sides by 9
x = 45/9
x = 5
Therefore, 5 teaspoons of red paint is needed to mix with 15 teaspoons of blue paint to make a purple paint.