2 : 7
(7/2) * 20
= 140/2
= 70 drops white paint to 20 drops red paint
====== Same for the other two problems; invert and multiply.
A color called passion pink is made by mixing red paint and white paint in a ratio of 2:7. How many drops of white paint do you need: if you use (20, 40, 3) drops of red paint?