Jackie's car radiator has a 9-liter capacity. The radiator contains a solution that is 20% antifreeze. To be safe, she would like the solution to contain 25% antifreeze. How much of the solution should she drain and replace with 100% antifreeze?
Look at the amount of antifreeze present.
if she drains x liters out, she needs
0.20(9-x) + x = 0.25*9
x = 0.5625