Question

Your automobile radiator contains 15 quarts of an antifreeze mixture.
A test shows the mixture is 40% antifreeze and 60% water. The owner's manual says the mixture should be 50% antifreeze and 50% water.

How much of the mixture should be removed and replaced with pure antifreeze so the final mixture is 50% antifreeze.

Answer 1

there should be 7.5 qt each of water and antifreeze

there are 9 qt of water ... .60 * 15 = 9

removing 1.5 qt of water from a 60% mix
... 1.5 = .60 * x ... 2.5 = x

remove 2.5 gal of the mixture and refill with pure antifreeze