Are all mixtures linear? I'm writing a computer program to help a factory produce bottles of mixtures. A mixture is usually alcohol, water and some other stuff, like menthol. But could also be water and NaOH and some oils (think schampoo).
My basic understanding is that if one bottle is 500 ml and contains:
50% water
45% alcohol
5% oils
I need:
250 ml water
225 ml alcohol
25 ml oils
Then if I want to make 1000 bottles I just multiply this with 1000:
250000 ml water
225000 ml alcohol
25000 ml oils
However this is with the assumption that all mixtures have linear dependencies.
So my questions is:

Is all (possible) mixtures linear?
Are all reactions linear?
Are there a difference between mixtures and solutions here?

I suspect this is a very easy question for someone who know chemistry, but unfortunately my understanding is basic and my search skills too bad to find this out.
Mixtures are never linear. Mixing $50$ mL water + $50$ mL ethanol gives a $96$ mL mixture. The masses are additive, but not the volumes. I agree the discrepancy is not huge. If you can tolerate a $10$% error, you may consider that the volumes are additive. Anyway take care of the fact that, usually percentage are indicated in mass, not in volume.