Question

How much pure acid should be mixed with 5 gallons of a 20% acid solution in order to get a 50% acid solution?

Answer 1

3 gallons

Explanation:

So we know that we're adding pure acid, so that would be 100%. We don't know how much pure acid we're adding, so we'll designate `x` to represent that quantity. Forming the equation, we get
`1.00x+0.20(5)=0.50(x+5)`
Simplifying, we get
`x+1=0.5x+2.5`
`x-0.5x=2.5-1`
`0.5x=1.5`
`x=3`
So we need 3 gallons of pure acid.