AN Automobile cooling system presently contains a mixture of water and anti freeze that freezes at 12 F. The owner recent moved and now needs protection against temperatures as low as -20 F. The manufacturer publishes a table which includes the fact that 12 F protection is provided with a 35% mixture, while -20 F protection requires an 80 % antifreeze mixture. How much should the owner drain off the his 9 liter coolant system and replace with pure antifreeze to get the required protection?

He starts with a 35% solution which is .35(9) antifreeze.

He drains out an x amount: .35(9-x)

And replaces it with the same amount of 100%: .35(9-x)+x

This must equal .8(9)

.35(9-x)+x=.8(9)

Solve for x.