I'll tackle #2 in a more logical, less algebraic approach than your other questions in your other thread.
You have 32% and 20% and you want to mix them to make 1 cup of 25%. Note that 25% is 5/12 of the way from 20 to 32. (32 - 20 = 12; 25 - 20 = 5). This means 5/12 of your mixture should be the 32% and 7/12 of the mixture should be the 20%. Makes sense - if you put equal amounts of each in, you'd get a percent right between the two, which is 26%. So, you want your chocolate not QUITE as strong (25% vs 26%), so use more of the weaker chocolate mix and less of the stronger.