Question

how many gallons of a 90% antifreeze solution must be mixed with 100 gallons of 30% antifreeze to get a mixture that is 80% antifreeze?

Answer 1

let the amount of 90% antifreeze to be added be x gallons

.9x + .3(100) = .8(100+x)
times 10
9x + 3(100) = 8(100+x)
9x+300 = 800+8x
x = 500

500 gallons of the 90% must be added.

Answer 2

450