1. The problem statement, all variables and given/known data In the materrials and methods of one article is mentioned that: A specific amount of citric acid and the catalyst sodium hypophosphite (50 % w/w, on weight of citric acid used) was dissolved in the starch solution. My question is how much citric acid and sodium hypophosphite I need to weigh on the balance? p.s: In one part of article is written: Films were cast from 3 % starch and cross-linked using 5 % (w/w) citric acid. 2. Relevant equations 3. The attempt at a solution 50 % w/w so we need to weigh 50 g or mg of citric acid + 50 g or mg of sodium hypophosphite. But why in another part of article mentioned 5 % of citric acid was used? I am confused!