Antifreeze in a car

Question

The radiator in a car is filled with a solution of 65% antifreeze and 35% water. The manufacturer of the antifreeze suggests that for summer driving, optimal cooling of the engine is obtained with only 50% antifreeze. If the capacity of the radiator is 4.6 liters, how much coolant (in liters) must be drained and replaced with pure water to reduce the antifreeze concentration to 50%?

Answer 1

4.6 liters of mix will contain 2.99 liters AF and 1.61 liters W (AF = Antifreeze & W = Water)

To get a 50% mix of antifreeze, you must have 2.3 liters AF & 2.3 liters W in the final mix.

So you must drain .69 liters of AF and therefore .3715 liters of W or 1.06154 liters of 65% antifreeze mix

Then you will have 2.3 liters of AF and 1.2385 liters W = 3.5385 liters total mix in the radiator

So, then add 1.06154 liters of W to get to now have 2.3 liters of W & 2.3 liters of AF for a 50% mix !