How much 90 percent vinegar do you have to add to a gallon of 5 percent vinegar to get 20 percent vinegar?

Question

I don't know how to do this.

Answer 1

How much 90 percent vinegar do you have to add to a gallon of 5 percent vinegar to get 20 percent vinega

(x)(90) + (1)(5) = (x + 1)(20)

90x + 5 = 20x + 20

70x = 15

x = .214 gal of the 90% vinegar