How many litres of pure antifreeze should be added to 5 litres of 30% antifreeze solution to create a 65% antifreeze solution?

Question

How many litres of pure antifreeze should be added to 5 litres of 30% antifreeze solution to create a 65% antifreeze solution?

Answer 1

1.00X + .30(5) = .65(5+X)

1.00X-.65X = 3.25 - 1.5 = 1.75

X = 1.75/.35 = 5 liters of pure antifreeze mixed with 30% antifreeze yield 10 liters of 65% antifreeze.

You could have noticed 100-65 = 35 and 65-30 = 35

65% is equidistant from 100 and 30, so you need equal amounts of each.