SOLUTION: The radiator in a certain make of car needs to contain 40 liters of 40% antifreeze. The radiator now contains 40 liters of 20% antifreeze. How many liters of this solution must be

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Question 730945: The radiator in a certain make of car needs to contain 40 liters of 40% antifreeze. The radiator now contains 40 liters of 20% antifreeze. How many liters of this solution must be drained and replaced with 100% antifreeze to get the desired strength?

Answer by josgarithmetic(39617) About Me  (Show Source):
You can put this solution on YOUR website!
You remove some volume, q of the 20% antifreeze. The amount of pure antifreeze in the tank is then 40*0.20-q*0.20 mass of pure antifreeze. Next q volume of the 100% antifreeze is added, so the amount of pure antifreeze in the tank becomes 40*0.20-q*0.20+q*1.00 mass of pure antifreeze.

All that was done so that the volume of antifreeze solution in the tank is again 40 liters of volume. NOW, we expect the result to be 0.40 or 40% antifreeze for that 40 liters.
%2840%2A0.20-q%2A0.20%2Bq%2A1.00%29%2F40=0.40, and you need to solve for q.