MIXING PAINTS

Hi, I'm new building models and I'm becoming crazy when I have to mix paints when I'm using airbrush. If I have to make this mix: XF-10:3 + X-10:2 I know that I need 3 drops of XF-10 and 2 drops of X-10.Questions: - Do I need exactly 5 drops of thinner?- If I'm using airbrush I will need more paint than painting with brush. Any advice to mix the exactly proportion of paint?? Using pipettes is crazy...Thanks,R.