Question

A mechanic needs a radiator to have 40% antifreeze solution. The radiator currently is filled with 5 gallons of 15% antifreeze solution.
How much antifreeze mixture should be drained from the car if the mechanic replaces it with pure antifreeze.

Drain__ gallons from the radiator.

Answer 1

let the amount drained be x gallons
These x gallons will contain .4x gallons of antifreeze

amount left of the old stuff = 5-x gallons
so ....

.15(5-x) + (1)x = .4(5)

solve for x

Let me know what you got, so I can check your answer.

Answer 2

x=2