A mechanic needs a radiator to have 50% antifreeze solution. the radiator currently is filled with 4 gallons of 15% antifreeze solution. how much antifreeze mixture should be drained from the car if the mechanic replaces it with pure antifreeze.

let x=gallons of current mixture to be drained and replaced with pure antifreeze.

4-x=gallons of current mixture remaining in the car.

0.15 (4-x) + 1.00x=0.50 x 4

0.6-.15x+x=2

0.85x=1.4

x=1.4/0.85 = 1.65 gal

Thus, 1.65 gallons of current mixture to be drained and replaced with pure antifreeze.