[learningworld]

Could you help with this one please? I’m stuck!
From a stock of 20% resin diluted in a mix of 2 solvents (5:1) I have lowered the concentration to 15% by adding 10ml of a different solvent onto 40ml of the initial stock. Which proportion do I have of these 3 solvents now?? And could you let me know how do I calculate this for future work please? Many thanks

[Orcio_87]

How to calculate - 80 % of 40 ml initial stock were the 2 solvents in ratio 5 to 1. Their quantity didn't change after the add 10 ml of third solvent, but concentration dropped by 50 / 40. Third solvent occupies 10 of 50 ml total volume.