Marcia has 2 liters of a 60% concentrated solution of phosphoric acid. She wants to add 3 liters of less concentrated phosphoric acid solutions, so that she has 5 liters of a solution with a concentration less than 50%. Which could she add? Indicate all possible combinations of solutions.

initial concentration = 60%

initial volume = 2 L

Final volume = 5 L

Final concentration required = Less than 50%

This is possible if we add a less concentrated solution of say concentration x%

5X (50) = 2 X 60 + 3 (x)

x = 43.33

So we have to add 3 L of solution with concentration less than 43.33%