Question

How much water must be evaporated from 130 gallons of a 9% acid solution to make a 12% acid solution?

Answer 1

Answer: 33 gallons

Explanation:

We initially have 130 gallons of a
`9\%` acid solution and we need to change it to a
`12\%` acid solution, and for that it is necessary to evaporate
`n` gallons of water.

So, this situation can be mathemtically expressed as follows:

`(130)(9\%)=(130-n)(12\%)`

Then:

`(130)((9)/(100))=(130-n)(1(12)/(100))`

Isolating
`n`:

`11.7=15.6-0.12 n`

`n=32.5 \approx 33`

Hence, we need to evaporate 33 gallons of water.