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The radiator in a car is filled with a solution of 70% antifreeze and 30% 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 3.5 L, how much coolant should be drained and replaced with water to reduce the antifreeze concentration to the recommended level?
water - water + water = water
0.30*3.5 - 0.30x + 1*x = 0.5*3.5
Multiply thru by 100 to get:
30*3.5 - 30x + 100x = 50*3.5
70x = 20*3.5
x = 1 liter (amt. of solution that should be replaced)