Question

How many gallons of 20% salt solution must be mixed with 4 gallons of 40% salt solution to make 25% salt solution?

Answer 1

If
`x` is the amount (gal) of the 20% solution to be used, then the mixture would have a total volume of
`x+4` gal. We want to end up with a 25% salt solution, so that

`0.2x+0.4\cdot4=0.25(x+4)`

`\implies0.2x+1.6=0.25x+1`

`\implies0.6=0.05x`

`\implies x=12`