Question

We have `25%` solution and a `50%` solution of a chemical. How do we mix them to prepare `100` gallons of `40%` solution?

Answer 1

`40` gallons of `25%` solution and `60` gallons of `50%` solution

Explanation:

The easiest way to solve questions relating to such mixtures is depicted in following diagram.

First write original strength as indicated in first row.
Then write desired strength in the center.
Then find the difference, using the cross.
This gives the ratio, in which original items should be mixed to get desired strength.

Here `25%` solution and a `50%` solution of the chemical should be mixed in the ratio of `2:3`

And as we desire `100` gallons of `40%` solution, we should have

`100xx2/5=40` gallons of `25%` solution and
`100xx3/5=60` gallons of `50%` solution