A scientist is mixing two solutions, Solution P and Solution Q. She uses 100 ml of Solution P and 200 ml of Solution Q. The total amount of solute in the final mixture is 50 grams. The equation $100p+200q=50$ represents this situation, where $p$ is the concentration of solute in Solution P (in grams per ml) and $q$ is the concentration of solute in Solution Q (in grams per ml). Which of the following is the best interpretation of $q$ in this context?